With a 4% survival rate at 5 years after diagnosis, pancreatic cancer is a devastating disease that remains essentially incurable with current therapeutic regimens and is the fourth leading cause of cancer mortality. Thus, there is a great need to identify novel cellular targets in pancreatic cancer cells that can be exploited for therapeutic benefit. In all tumor cells, including pancreatic cancer cells, transition across cell cycle checkpoints is dependent on activation of cyclin:Cdk complexes by Cdk Activating Kinase (CAK). CAK represents a potential novel Achilles'heel type of target for therapeutic intervention treatment in pancreatic cancer that would impact many positions in the cell cycle. However, the identity of CAK remains unclear. A high molecular weight CAK complex was previously identified as cyclin H:Cdk7;however, cyclin H:cdk7 is also the bona fide kinase in TFIIH, a kinase that activates RNA polymerase II for initiation of transcription. Consequently, all experiments that disrupted the putative CAK activity of Cdk7 also resulted in global disruption of transcriptional elongation by Cdk7 TFIIH, thereby making interpretation problematic. Moreover, we find that selective inactivation of Cdk7 in cells results in the maintenance of in vivo CAK activity and thereby questions Cdk7's role as a CAK. Previously, we have detected a second Low Molecular Weight CAK activity that is entirely independent of Cdk7. Our central hypothesis is that the low molecular weight complex contains the relevant Cdk Activating Kinase (CAK) that phosphorylates and activates cyclin:Cdk complexes required to drive pancreatic cancer cells across cell cycle checkpoints. If correct, this CAK is a potential novel therapeutic target for the treatment of pancreatic cancer whose inactivation would simultaneously affect multiple cell cycle checkpoints. Our goal for this R21 exploratory application is to isolate the Low Mw CAK gene(s) and determine if CAK is rate-limiting for cyclin:Cdk activation.
Aim 1 : Biochemically Purify and Identify the Low Mw CAK Gene(s) We will isolate the Low Mw CAK complex from Panc1 pancreatic cancer cells that contain constitutively active Cdk2, and hence, by definition, also contain constitutively express CAK, and identify it's sequence by mass spectrometry and confirm by RNAi.
Aim 2. Unbiased RNAi Screen to Identify the CAK Gene(s) from Pancreatic Cells. We will perform an unbiased kinome RNAi screen in Panc1 pancreatic cancer cells. There are ~448 proven and putative Ser/Thr kinases in the human genome and therefore, this is manageable as a low throughput, but high information generating RNAi screen using a high validated, high titer lentiviral shRNA library.
Pancreatic cancer is a devastating disease that is essentially incurable with current therapeutic approaches. Like the vast majority of tumors, pancreatic cancer cells select for deregulation of cellular checkpoints that ultimately impinge on activation of cyclin:Cdk complexes by a likely oncogene, the Cdk Activating Kinase (CAK). The identity of CAK remains unclear and this project will determine the identity of CAK in pancreatic cancer.
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