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Since type and duration of an appropriate adjuvant chemotherapy in early-stage ovarian cancer (OC) are still being debated, novel markers for a better stratification of these patients are of utmost importance for the design of an improved chemotherapeutical strategy. In contrast to numerous cancer studies on cellular proliferation based on the immunohistochemistry-driven evaluation of protein expression, we compared mRNA and protein expression of two independent markers of cellular proliferation, Ki-67 and Plk1, in a large cohort of 243 early-stage OC and their relationship with clinicopathological features and survival. Based on marker expression we demonstrate that early-stage OC patients (stages I/II, low-grade, serous) with high expression (Ki-67, Plk1) had a significantly shorter progression-free survival (PFS) and overall survival (OS) compared to patients with low expression (Ki-67, Plk1). Remarkably, based on mRNA expression this significant difference got lost in advanced stages (III/IV): At least for PFS, high levels of Ki-67 and Plk1 correlate with moderately better survival compared to patients with low expressing tumors. Our data suggest that in addition to Ki-67, Plk1 is a novel marker for the stratification of early-stage OC patients to maximize therapeutic efforts. Both, Ki-67 and Plk1, seem to be better suited in early-stages (I/II) as therapeutical targets compared to advanced-stages (III/IV) OC.
Ligand stimulation of CD95 induces activation of Plk3 followed by phosphorylation of caspase-8
(2016)
Upon interaction of the CD95 receptor with its ligand, sequential association of the adaptor molecule FADD (MORT1), pro-forms of caspases-8/10, and the caspase-8/10 regulator c-FLIP leads to the formation of a death-inducing signaling complex. Here, we identify polo-like kinase (Plk) 3 as a new interaction partner of the death receptor CD95. The enzymatic activity of Plk3 increases following interaction of the CD95 receptor with its ligand. Knockout (KO) or knockdown of caspase-8, CD95 or FADD prevents activation of Plk3 upon CD95 stimulation, suggesting a requirement of a functional DISC for Plk3 activation. Furthermore, we identify caspase-8 as a new substrate for Plk3. Phosphorylation occurs on T273 and results in stimulation of caspase-8 proapoptotic function. Stimulation of CD95 in cells expressing a non-phosphorylatable caspase-8-T273A mutant in a rescue experiment or in Plk3-KO cells generated by CRISPR/Cas9 reduces the processing of caspase-8 prominently. Low T273 phosphorylation correlates significantly with low Plk3 expression in a cohort of 95 anal tumor patients. Our data suggest a novel mechanism of kinase activation within the Plk family and propose a new model for the stimulation of the extrinsic death pathway in tumors with high Plk3 expression.