Phosphorylation of Pit-1 by Cyclin-Dependent Kinase 5 at Serine 126 is Associated with Cell Proliferation and Poor Prognosis in Prolactinomas

Abstract Background Pit-1 is a POU-homeodomain transcription factor, and cyclin-dependent kinase 5 (CDK5) is a protein kinase that can phosphorylate many key transcription factors, but the mechanism by which CDK5 phosphorylates Pit-1 is unclear.Methods We generated an antibody that specifically recognizes phosphorylated the serine at position 126 of Pit-1 (Ser126-Pit-1); we used western blotting to detect the level of Pit-1 phosphorylation and observed the proliferation and apoptosis of GH3 cells with different levels of Pit-1 phosphorylation by clone formation experiments, cell viability assays, and flow cytometry. ELISA was used to measure the level of prolactin (PRL) in the supernatant of GH3 cells. Tissue microarrays and immunohistochemistry (IHC) were used to evaluate the expression of the phosphorylation level of Ser126-Pit-1 (pSer126-Pit-1) in prolactinomas. Results Our data indicated that Ser126-Pit-1 is specifically phosphorylated by CDK5. pSer-126-Pit-1 can promote cell proliferation and PRL secretion. Besides, a higher level of pSer-126-Pit-1 correlates with a worse prognosis in patients with prolactinoma. Conclusions CDK5 mediated Ser126-Pit-1 phosphorylation regulates prolactinoma progression and PRL secretion.