Targeting the RNA Splicing Machinery as a Novel Treatment Strategy for Pancreatic Carcinoma

Abstract

Aberrant patterns of pre-mRNA splicing have been established for many human malignancies, yet the mechanisms responsible for these tumor-specific changes remain undefined and represent a promising area for therapeutic intervention. Using immunohistochemistry, we have localized the expression of a central splicing regulator, serine-arginine protein kinase 1 (SRPK1), to the ductular epithelial cells within human pancreas and have further shown its increased expression in tumors of the pancreas, breast, and colon. Small interfering RNA-mediated down-regulation of SRPK1 in pancreatic tumor cell lines resulted in a dose-dependent decrease in proliferative capacity and increase in apoptotic potential. Coordinately, the disruption of SRPK1 expression resulted in enhanced sensitivity of tumor cells to killing by gemcitabine and/or cisplatin. A dose-dependent reduction in the phosphorylation status of specific SR proteins was detected following the downregulation of SRPK1 and is likely responsible for the observed alterations in expression of proteins associated with apoptosis and multidrug resistance. These data support SRPK1 as a new, potential target for the treatment of pancreatic ductular cancer that at present remains largely unresponsive to conventional therapies. Furthermore, these results support the development of innovative therapies that target not only specific splice variants arising during tumorigenesis but also the splice regulatory machinery that itself may be abnormal in malignant cells.

Regulation of SR protein phosphorylation and alternative splicing by modulating kinetic interactions of SRPK1 with molecular chaperones

“…6F). These observations corroborate the genetic evidence that SRPKs are major kinases for SR proteins in mammalian cells as their siRNA-mediated down-regulation (Hayes et al 2006) or inactivation by homologous recombination (P.-P. Wang and X.-D. Fu, unpubl.) both attenuated SR protein phosphorylation.…”

“…It is thus not surprising that experimental induction of both hypo-and hyperphosphorylation of SR proteins frustrates this cycle and inhibits splicing, an outcome that underscores the requirement for precise regulation of SR protein phosphorylation in the cell (Prasad et al 1999). Despite that multiple protein kinases and phosphatases have been implicated in SR protein phosphorylation and dephosphorylation, only SRPK1 and PP1 have been characterized by RNAi-mediated knockdown (Hayes et al 2006;Shi and Manley 2007). While a recent study demonstrated the activation of PP1 by stripping off a heatshock-sensitive PP1 inhibitor and showed that the phosphorylation state of different SR proteins is controlled by both activated PP1 and differential accessibility of SR protein kinases (Shi and Manley 2007), little is known about how specific SR kinases might be regulated under physiological conditions.…”

E2F1 controls alternative splicing pattern of genes involved in apoptosis through upregulation of the splicing factor SC35

“…34,35 However, the molecular mechanisms involved in such processes remain largely unknown. Importantly, and consistent with a function of SR proteins during the response to DNA damage, it has been previously shown that SC35 accumulates following g-irradiation.…”

Gemcitabine triggers a pro-survival response in pancreatic cancer cells through activation of the MNK2/eIF4E pathway

“…In this regard, it is noteworthy that the SR protein kinase 1, a key regulator of SRSF1 activity, is also upregulated in PDAC 28 and was proposed as a suitable target for novel therapies. 29 In conclusion, our study identifies a novel pro-survival pathway triggered by gemcitabine in PDAC cells, which relies on MNK2-dependent phosphorylation of eIF4E, and suggests that targeting this pathway might represent a promising approach to enhance the response of PDAC cells to therapeutic agents.…”