SASH1 (SAM [sterile alpha motif] and SH3 [SRC-homology-3] domain-containing protein 1) is a multidomain scaffold implicated in pigmentation, innate immunity, receptor signaling, cytoskeletal dynamics, vascular biology, and tumor suppression. Although genetic and expression studies link SASH1 dysfunction to diverse diseases, a unifying mechanistic framework has remained elusive. Here, we synthesize current knowledge of SASH1 structure, interaction networks, and biological functions across cell types and disease contexts. SASH1 contains an intrinsically disordered SPIDER (SLy Proteins Associated Disordered Region), an SH3 domain, two SAM domains, and multiple linear motifs; together, these elements mediate interactions with EphA8 (ephrin type-A receptor 8), β-arrestin 1, TRAF6 (TNF receptor-associated factor 6), CRKL (CRK-like proto-oncogene), IQGAP1 (IQ-motif-containing GTPase-activating protein 1), cortactin, and TNKS2 (tankyrase-2). We propose that SASH1 functions as a context-dependent multi-docking scaffold that organizes signaling architecture. Its modular domains, intrinsically disordered regions, and dual SAM domains enable flexible, multivalent interactions with partners that can be grouped into three functional modules: receptor regulation, intracellular signaling, and cytoskeletal organization. Notably, many SASH1 partners are themselves scaffold or adaptor proteins, allowing integration into pre-existing networks in a hierarchical ‘scaffold-of-scaffolds’ manner. Through selective partner recruitment, SASH1 links cell-surface receptor inputs to downstream signaling pathways and cytoskeletal remodeling. This model provides a mechanistic framework for how SASH1 drives diverse, cell-type-specific outputs across physiology and disease, while revealing broader principles by which multidomain scaffolds encode cellular behavior.

The BCL2 family of proteins plays a pivotal role in regulating apoptosis and cellular homeostasis, making them critical therapeutic targets in cancer and other diseases characterized by pathological cell survival. BH3 mimetics, small molecules that selectively inhibit anti-apoptotic BCL2 family members, have achieved significant clinical success, particularly in hematologic malignancies. However, several challenges remain, including resistance mechanisms, toxicity (such as MCL1 inhibitor-associated cardiotoxicity), and the intricate balance between apoptotic and non-apoptotic functions. This review provides a comprehensive overview of BCL2 family biology, the development and clinical application and outcomes of BH3 mimetics, and the emerging resistance mechanism known as double-bolt locking. We also examine strategies to overcome resistance, including combination therapies and immunomodulatory approaches. Beyond oncology, we highlight the expanding therapeutic potential of BH3 mimetics in autoimmune, fibrotic, and infectious diseases, as well as regenerative and anti-aging medicine. Finally, we discuss predictive biomarkers and tissue-specific responses that inform precision therapy. Together, these insights underscore the promise of BH3 mimetics and the need for continued multidisciplinary research to optimize their clinical impact.

Both aging spots (hyperpigmentation) and hair graying (lack of pigmentation) are associated with aging, two seemingly opposite pigmentation phenotypes. It is not clear how they are mechanistically connected. This study investigated the underlying mechanism in a family with an inherited pigmentation disorder. Clinical examinations identified accelerated hair graying and skin dyspigmentation (intermixed hyper and hypopigmentation) in the family members carrying the SASH1 S519N variant. Cell assays indicated that SASH1 promoted stem-like characteristics in human melanocytes, and SASH1 S519N was defective in this function. Multiple assays showed that SASH1 binds to tankyrase 2 (TNKS2), which is required for SASH1's promotion of stem-like function. Further, the SASH1 S519N variant is in a bona fide Tankyrase-binding motif, and SASH1 S519N alters the binding kinetics and affinity. Results here indicate SASH1 as a novel protein regulating the appropriate balance between melanocyte stem cells (McSC) and mature melanocytes (MCs), with S519N variant causing defects. We propose that dysfunction of McSC maintenance connects multiple aging-associated pigmentation phenotypes in the general population.

A better understanding of human melanocyte (MC) and melanocyte stem cell (McSC) biology is essential for treating melanocyte-related diseases. This study employed an inherited pigmentation disorder carrying the SASH1S519N variant in a Hispanic family to investigate the SASH1 function in the MC lineage and the underlying mechanism for this disorder. We used a multidisciplinary approach, including clinical exams, human cell assays, yeast two-hybrid screening, and biochemical techniques. Results linked early hair graying to the SASH1S519N variant, a previously unrecognized clinical phenotype in hyperpigmentation disorders. In vitro, we identified SASH1 as a regulator in McSC maintenance and discovered that TNKS2 is crucial for SASH1’s role. Additionally, the S519N variant is located in one of multiple tankyrase-binding motifs and alters the binding kinetics and affinity of the interaction. In summary, this disorder links both gain and loss of pigmentation in the same individual, hinting to accelerated aging in human McSC. The findings offer insights into the roles of SASH1 and TNKS2 in McSC maintenance and the molecular mechanisms of pigmentation disorders. We propose that a comprehensive clinical evaluation of patients with MC-related disorders should include an assessment and history of hair pigmentation loss.

Immune checkpoint inhibitors (ICIs) are now the first-line treatment for patients with advanced melanoma. Despite promising clinical results, many patients fail to respond to these therapies. BH3 mimetics, a novel class of small molecule inhibitors that bind and inhibit anti-apoptotic members of the BCL2 family proteins such as BCL2 or MCL1, have been very successful in treating hematologic malignancies. However, there are limited studies on the immunomodulatory role of the BH3 mimetics. Several factors contribute to ICI resistance including myeloid-derived suppressor cells (MDSCs) that exert immunosuppressive effects through direct and indirect inhibition of antitumor immunity. Thus, targeting MDSCs to enhance antitumor immunity has the potential to enhance the efficacy of ICIs. In this study, we show that the MCL1 inhibitor S64315 reduces melanoma tumor growth in an immune cell-dependent manner in mice. Specifically, S64315 enhances antitumor immunity by reducing MDSC frequency and by promoting the activity of CD8+T cells. Additionally, human MDSCs are 10 times more sensitive to S64315 than cutaneous melanoma lines. Further, we found that a higher expression of MCL1 is associated with poor survival for patients treated with anti-PD-1. Finally, combining S64315 and anti-PD-1 significantly slowed tumor growth compared to either agent alone. Together, this proof-of-concept study demonstrates the potential of combining an MCL1 inhibitor with anti-PD-1 in the treatment of melanoma. It justifies the further development of next generation MCL1 inhibitors to improve efficacy of ICIs in treating malignant melanoma.

Non-specific immunoblot bands in MB 1692 and MB 1374

Expression of ALKATI and EML4-ALK isoforms in PDX vs xenografts

Melanoma remains a significant and rising health burden. Currently most melanoma patients are treated with immunotherapies, but almost half do not respond to, or relapse from the treatments. One of the main contributors to immunotherapy resistance is an immunosuppressive cell population, called myeloid-derived suppressive cells (MDSCs). Therefore, enhancing the efficacy of immunotherapies by targeting MDSCs represents a promising strategy to improve overall outcomes. One unexplored mechanism is regulating tumor and immune cell survival using BH3 mimetics. BH3 mimetics are small molecule therapies that block the anti-apoptotic function of BCL2 family proteins in cancer cells, resulting in cell death. MCL1 is a pro-survival member of the BCL2 family. Our recent study suggests BH3 mimetics such as MCL1 inhibitor (MCL1i) can induce apoptosis in uveal melanoma in vitro and in vivo. This study aimed to investigate how MCL1i influence the efficacy of immunotherapy. We examined the transcriptional profile of tumor-associated myeloid cells from two melanoma patients who relapsed from anti-PD1 treatment using single-cell RNA-sequencing. We found that MDSCs displayed the excessive MCL1 expression, suggesting inhibiting MCL1 may be a rational strategy to target MDSCs and improve immunotherapies. To test this possibility, we examined the effects of MCL1i using the syngeneic model B16 mouse melanoma cell line in immunocompetent C57B6 mice. We found that MCL1i decreased the frequency of tumor infiltrating MDSCs, while increasing the frequency and activation of CD8+ T cells. Further, MCL1i enhanced the efficacy of anti-PD-1 immunotherapy and the combination treatment significantly delayed tumor growth in mouse compared to either single drug treatment. Taken together, this study indicates MCL1i are promising candidates to improve the efficacy of immunotherapies for melanoma.

ALK qRT-PCR screen in melanoma PDX models

Additional ALK inhibitor testing and IC50 values

Tankyrases, a versatile protein group within the poly(ADP-ribose) polymerase family, are essential for post-translational poly(ADP-ribosyl)ation, influencing various cellular functions and contributing to diseases, particularly cancer. Consequently, tankyrases have become important targets for anti-cancer drug development. Emerging approaches in drug discovery aim to disrupt interactions between tankyrases and their binding partners, which hinge on tankyrase-binding motifs (TBMs) within partner proteins and ankyrin repeat cluster domains within tankyrases. Our study addresses the challenge of identifying and ranking TBMs. We have conducted a comprehensive review of the existing literature, classifying TBMs into three distinct groups, each with its own scoring system. To facilitate this process, we introduce TBM Hunter—an accessible, web-based tool. This user-friendly platform provides a cost-free and efficient means to screen and assess potential TBMs within any given protein. TBM Hunter can handle individual proteins or lists of proteins simultaneously. Notably, our results demonstrate that TBM Hunter not only identifies known TBMs but also uncovers novel ones. In summary, our study offers an all-encompassing perspective on TBMs and presents an easy-to-use, precise, and free tool for identifying and evaluating potential TBMs in any protein, thereby enhancing research and drug development efforts focused on tankyrases.

Overexpression of EML4-ALK, ALKATI, and wtALK in NIH3T3

SAM domains are crucial mediators of diverse interactions, including those important for tumorigenesis or metastasis of cancers, and thus SAM domains can be attractive targets for developing cancer therapies. This review aims to explore the literature, especially on the recent findings of the structural dynamics, regulation, and functions of SAM domains in proteins containing more than one SAM (multi-SAM containing proteins, MSCPs). The topics here include how intrinsic disorder of some SAMs and an additional SAM domain in MSCPs increase the complexity of their interactions and oligomerization arrangements. Many similarities exist among these MSCPs, including their effects on cancer cell adhesion, migration, and metastasis. In addition, they are all involved in some types of receptor-mediated signaling and neurology-related functions or diseases, although the specific receptors and functions vary. This review also provides a simple outline of methods for studying protein domains, which may help non-structural biologists to reach out and build new collaborations to study their favorite protein domains/regions. Overall, this review aims to provide representative examples of various scenarios that may provide clues to better understand the roles of SAM domains and MSCPs in cancer in general.

Characterization of EML4-ALK fusion variants in MB 2141

SASH1 is a scaffold protein with context-dependent biological functions in cell adhesion, tumor metastasis, lung development, and pigmentation. As a member of the SLy protein family, it contains the conserved SLY, SH3, and SAM domains. The 19 kDa SLY domain harbors over 70% of the SASH1 variants associated with pigmentation disorders. However, its solution structure or dynamics have not been investigated yet, and its exact position in the sequence is not clearly defined. Based on the bioinformatic and experimental evidence, we propose renaming this region to the SLy Proteins Associated Disordered Region (SPIDER) and defining the exact position to be amino acids 400-554 of SASH1. We have previously identified a variant in this region linked to a pigmentation disorder, S519N. Here, we used a novel deuteration technique, a suite of TROSY-based 3D NMR experiments, and a high-quality HNN to obtain near complete solution backbone assignment of SASH1's SPIDER. A comparison with the chemical shifts of non-variant (S519) SPIDER shows that the S519N substitution does not alter the free form solution structural propensities of SPIDER. This assignment is the first step to characterize the role of SPIDER in SASH1-mediated cellular functions and provides a model for the future study of sister SPIDER domains in the SLy protein family.

The sterile alpha motif (SAM) domains are among the most versatile protein domains in biology, and the variety of the oligomerization states contribute to their diverse roles in many diseases. A better understanding of the structure and dynamics of various SAM domains will provide a scientific basis for drug development targeting them. Here, we used SEC-MALS, HPLC, NMR, and other biophysical techniques to characterize the structural features and dynamics of the SAM1 domain in SASH1. SASH1 is a scaffold protein belonging to the same family as SASH3. Unlike the dimerization seen in SASH3's SAM domain, our SEC-MALS and SE-HPLC showed that SAM1 exists primarily as a less compact monomer with a minor oligomer. NMR assignment, relaxation, and exchange experiments revealed the presence of both a disordered monomer and a more structured oligomer with multiple timescale exchange regimes in solution. Mutagenesis and SE-HPLC showed that D663A/T664K substitutions in SAM1 increased its oligomerization. In sum, this study is the first to characterize a disordered structure for a SAM domain, provides additional evidence and framework for the diversity of SAM domains, and identifies a region in SAM1 as a potential starting point to further characterize the structural mechanism of oligomerization of the domain.

The two subtypes of melanomas, uveal (UM) and cutaneous (CM), originate from melanocyte transformation, but differ in their genetic etiology and signaling pathways. MCL1 and BCL2, the anti-apoptotic members of the BCL2 family, induce anti-cancer treatment resistance. Here, we evaluate their basal levels and role in inducing response to MCL1 inhibitor (MCL1i) in CM and UM. We used in vitro assays (viability, immunoblot and shRNA), and bioinformatics analyses of the TCGA database. UM cell lines have higher BCL2 and lower MCL1 protein expressions compared to CM. Mechanistic studies using shRNAs suggest knockdown (KD) of MCL1 in UM led to ∼30% reduction in cell viability and sensitized them to MCL1i (p<0.001); however, KD of MCL1 in CM did not significantly alter viability or sensitivity to MCL1i. KD of BCL2 did not have significant effect in either CM or UM. Thus, MCL1 may play a larger role in UM, and to further understand, we looked at the binding partners of MCL1: BOK, BAK, BIM, NOXA and PUMA. UM had higher BOK, BAK and PUMA and lower BIM and NOXA compared to CM. KD of PUMA and BIM led to partial protection against MCL1i induced cell death in multiple UM cell lines (p<0.05), while the effects of KD of NOXA were variable. Further studies with KD of BAK and BOK are in progress. Results suggest low MCL1 expression and high pro-apoptotic BCL2 family members that bind to MCL1 contributes to a high sensitivity of UM to MCL1 inhibitors. To determine the clinical relevance, we analyzed the gene expression of TCGA database of 34 cancer types. UM had much higher expression of BCL2, BOK and PUMA and lower MCL1, NOXA and BIM compared to CM (p<0.001). In addition, UM had the highest level of BCL2 and PUMA. Thus, our studies with cell lines are consistent with clinical samples. Overall, our data indicates that the basal level of MCL1 and its binding partners contributes to differences in UM and CM's response to MCL1i, and UM is a good candidate for treatment with MCL1 inhibitors.

Uveal melanoma (UM) is a subtype of melanoma. Although they share a melanocytic origin with cutaneous melanoma (CM), patients with UM have few treatment options. BCL2 homologous 3 mimetics are small-molecule drugs that mimic proapoptotic BCL2 family members. We compared BCL2 family member expression between UM and CM using immunoblot and The Cancer Genome Atlas transcriptomic analysis. UM has a unique signature of low BFL1 and high PUMA proteins compared with CM and 30 other cancer types, making them an attractive candidate for BCL2 homologous 3 protein mimetics. We tested the efficacy of a BCL2 inhibitor and MCL1 inhibitor (MCL1i) in UM, with viability assays, live-cell imaging, sphere assays, and mouse xenograft models. UM had a higher sensitivity to MCL1i than CM. Overexpression of BFL1 or knockdown of PUMA made the UM more resistant to MCL1i. In contrast, MAPK/extracellular signal‒regulated kinase inhibitor treatment in CM made them more sensitive to MCL1i. However, MCL1i-alone treatment was not very effective to reduce the UM initiating cells; to overcome this, we employed a combination of MCL1i with BCL2 inhibitor that synergistically inhibited UM initiating cell's capacity to expand. Overall, we identify a distinct expression profile of BCL2 family members for UM that makes them susceptible to BCL2 homologous 3 mimetics.