The polycomb group protein, BMI1 plays important roles in chromatin modification, stem cell function, DNA damage repair and mitochondrial bioenergetics. Such diverse cellular functions of BMI1 could be, in part, due to post-translational modifications, especially phosphorylation. To date, AKT has been reported as a kinase that by site specific phosphorylation of BMI1 modulates its oncogenic functions. Immunoprecipitation in conjunction with kinase assay and mass spectrometry was used to determine association with and site specific phosphorylation of BMI1 by CK2α. Functional implications of the BMI1/CK2α axis was examined in cancer cells utilizing siRNA and exogenous gene expression followed by biochemical and phenotypic studies. Correlations between expression of CK2α and BMI1 were determined from cell lines and formalin fixed paraffin embedded tissues representing the normal fallopian tube epithelium and high grade serous ovarian cancer samples. Here we report that CK2α, a nuclear serine threonine kinase, phosphorylates BMI1 at Serine 110 as determined by in-vitro/ex-vivo kinase assay and mass spectrometry. In ovarian cancer cell lines, expression of CK2α correlated with the phospho-species, as well as basal BMI1 levels. Preventing phosphorylation of BMI1 at Serine 110 significantly decreased half-life and stability of the protein. Additionally, re-expression of the phosphorylatable but not non-phosphorylatable BMI1 rescued clonal growth in endogenous BMI1 silenced cancer cells leading us to speculate that CK2α-mediated phosphorylation stabilizes BMI1 and promotes its oncogenic function. Clinically, compared to normal fallopian tube epithelial tissues, the expression of both BMI1 and CK2α were significantly higher in tumor tissues obtained from high-grade serous ovarian cancer patients. Among tumor samples, the expression of BMI1 and CK2α positively correlated (Spearman coefficient = 0.62, P = 0.0021) with each other. Taken together, our findings establish an important regulatory role of CK2α on BMI1 phosphorylation and stability and implicate the CK2α/BMI1 axis in ovarian cancer.

Methotrexate and actinomycin-D are both effective first-line drugs for low-risk (WHO score 0-6) Gestational Trophoblastic Neoplasia (GTN) with considerable debate about which is more effective, less toxic, and better tolerated. The primary trial objective was to test if treatment with multi-day methotrexate (MTX) was inferior to pulse actinomycin-D (ACT-D). Secondary objectives included evaluation of severity and frequency of adverse events, and impact on quality of life (QOL). This was a prospective international cooperative group randomized phase III two arm non-inferiority study (Clinical Trials Identifier: (NCT01535053). The control arm was ACT-D; the experimental arm was multi-day MTX regimen (institutional preference of 5 or 8 day). Outcome measures included complete response rate, recurrence rate, toxicity, and QOL as measured by FACT-G and FACIT supplemental items. The complete response rates for multi-day methotrexate and pulse actinomycin-D were 88% (23/26 patients) and 79% (22/28 patients) (p = NS) respectively, there were two recurrences in each arm, and 100% of patients survived. Significant toxicity was minimal, but mouth sores (mucositis), and eye pain were significantly more common in the MTX arm (p = 0.001 and 0.01 respectively). Quality of life showed no significant difference in overall quality of life, body image, sexual function, or treatment related side effects. The study was closed for low accrual rate (target 384, actual accrual 57), precluding statistical analysis of the primary objective. The complete response rate for multi-day methotrexate was higher than actinomycin-D, but did not reach statistical significance. The multi-day MTX regimens were associated with significantly more mucositis and were significantly less convenient.