The non-apoptotic function of Caspase-8 in negatively regulating the CDK9-mediated Ser2 phosphorylation of RNA polymerase II in cervical cancer

Abstract

Cervical cancer is the fourth most frequently diagnosed and fatal gynecological cancer. 15–61% of all cases metastasize and develop chemoresistance, reducing the 5-year survival of cervical cancer patients to as low as 17%. Therefore, unraveling the mechanisms contributing to metastasis is critical in developing better-targeted therapies against it. Here, we have identified a novel mechanism where nuclear Caspase-8 directly interacts with and inhibits the activity of CDK9, thereby modulating RNAPII-mediated global transcription, including those of cell-migration- and cell-invasion-associated genes. Crucially, low Caspase-8 expression in cervical cancer patients leads to poor prognosis, higher CDK9 phosphorylation at Thr186, and increased RNAPII activity in cervical cancer cell lines and patient biopsies. Caspase-8 knock-out cells were also more resistant to the small-molecule CDK9 inhibitor BAY1251152 in both 2D- and 3D-culture conditions. Combining BAY1251152 with Cisplatin synergistically overcame chemoresistance of Caspase-8-deficient cervical cancer cells. Therefore, Caspase-8 expression could be a marker in chemoresistant cervical tumors, suggesting CDK9 inhibitor treatment for their sensitization to Cisplatin-based chemotherapy.

Prognostic Impact of Caspase-8, CDK9 and Phospho-CDK9 (Thr 186) Expression in Patients with Uterine Cervical Cancer Treated with Definitive Chemoradiation and Brachytherapy

“…Interactome analyses have indicated a novel interaction between caspase-8 and CDK9 in cervical cancer cell lines and patient-derived organoids [ 19 ], where the loss/attenuation of caspase-8 induces an overactivation of CDK9, which subsequently alters the cellular transcriptional landscape (transcriptional reprogramming) [ 19 ]. On a molecular level, caspase-8 allosterically inhibits the (auto)phosphorylation of CDK9 at Thr 186 (pCDK9) [ 45 , 46 ], thereby compromising its activation and, consequently, the activity of the CDK9/CyclinT1 complex-P-TEFb in phosphorylating the Ser2 residue at the C-terminal domain (CTD) of RNAPII [ 20 ].…”

“…This modulation in RNAPII’s activity results in altered cellular transcription, especially in the expression levels of several genes involved in migration and invasion, providing strong evidence for the substantial role of capsase-8 in suppressing metastasis in cervical cancer. Further, the knock-out/attenuation of caspase-8 resulted in a significant enhancement of 2D cell migration and 3D cell invasion in favor of the involvement of caspase-8 in the regulation of transcriptional metastases in cervical cancer [ 19 ]. As stated before, and in support of these mechanistic findings, for the first time, we report an inverse correlation between Thr 186 phosphorylation of CDK9 and caspase-8 and, as expected, with CDK9 immunoexpression, in the clinical setting.…”

“…As a result, cancer cells regularly attempt to evade caspase-8-induced cell death through post-translational modifications [ 14 , 15 , 16 ], loss-of-function mutations of pro-apoptotic genes and the overexpression of anti-apoptotic genes or the expression of FLICE-like inhibitory protein long FLIPL [ 10 , 17 , 18 ]. Recent evidence has further highlighted the non-apoptotic properties of caspase-8, including its involvement in cell-cycle regulation, proliferation, angiogenesis, cell migration, cell invasion and resistance to chemotherapy [ 10 , 11 , 13 , 19 ]. As a result, the downregulation of caspase-8’s activity has been shown to be beneficial for several malignancies, which can be traced back to its non-apoptotic functions.…”

“…We have recently also identified a novel mechanism where nuclear caspase-8 directly interacts with and inhibits the activity of cyclin-dependent kinase 9 (CDK9), thereby modulating RNA polymerase II (RNAPII)-mediated global transcription, including that of metastasis-associated genes [ 19 ]. Essentially, caspase-8 negatively regulates the autophosphorylation of CDK9 at Thr 186 (pCDK9), compromising its activation and the activity of the CDK9/CyclinT1-p-TEFb (Positive Transcription Elongation Factor b) complex.…”

“…The latter phosphorylates the serine (Ser)2 residue of the YSPTSPS tandem repeats at the C-terminus domain (CTD) of RNAPII to promote transcriptional elongation [ 20 ]. As a result, loss of caspase-8 may lead to the hyperactivated state of CDK9, altering the transcriptional landscape of cervical cancer towards a more aggressive phenotype [ 19 , 21 ].…”