Abnormal Expression of the Pre-mRNA Splicing Regulators SRSF1, SRSF2, SRPK1 and SRPK2 in Non Small Cell Lung Carcinoma

Abstract

Splicing abnormalities frequently occur in cancer. A key role as splice site choice regulator is played by the members of the SR (Ser/Arg-rich) family of proteins. We recently demonstrated that SRSF2 is involved in cisplatin-mediated apoptosis of human lung carcinoma cell lines. In this study, by using immunohistochemistry, we demonstrate that the SR proteins SRSF1 and SRSF2 are overexpressed in 63% and 65% of lung adenocarcinoma (ADC) as well as in 68% and 91% of squamous cell lung carcinoma (SCC), respectively, compared to normal lung epithelial cells. In addition, we show that SRSF2 overexpression correlates with high level of phosphorylated SRSF2 in both ADC (p<0.0001) and SCC (p = 0.02), indicating that SRSF2 mostly accumulates under a phosphorylated form in lung tumors. Consistently, we further show that the SR-phosphorylating kinases SRPK1 and SRPK2 are upregulated in 92% and 94% of ADC as well as in 72% and 68% of SCC, respectively. P-SRSF2 and SRPK2 scores are correlated in ADC (p = 0.01). Using lung adenocarcinoma cell lines, we demonstrate that SRSF1 overexpression leads to a more invasive phenotype, evidenced by activation of PI3K/AKT and p42/44MAPK signaling pathways, increased growth capacity in soft agar, acquisition of mesenchymal markers such as E cadherin loss, vimentin and fibronectin gain, and increased resistance to chemotherapies. Finally, we provide evidence that high levels of SRSF1 and P-SRSF2 proteins are associated with extensive stage (III–IV) in ADC. Taken together, these results indicate that a global deregulation of pre-mRNA splicing regulators occurs during lung tumorigenesis and does not predict same outcome in both Non Small Cell Lung Carcinoma histological sub-types, likely contributing to a more aggressive phenotype in adenocarcinoma.

Dysregulation of splicing proteins in head and neck squamous cell carcinoma

“…41 Studies have reported SRPK1 and SRPK2 to be overexpressed in non-small cell lung cancer and their overexpression correlated with hyperphosphorylation of SRSF1 and SRSF2. 13 In concurrence with these studies, our data reveals both hyperphosphorylation and overexpression of SRPK2 in HNSCC cell lines. Taken together, these studies highlight the crucial role of SRPKs and their substrates in the regulation of splicing in cancer.…”

“…11,12 Aberrant activation or expression of splice factors and kinases has been shown to influence cellular transformation and other oncogenic processes. 13,14 Among the proteins involved in splicing, we identified hyperphosphorylation of SRPK2, a splicing kinase known to affect subcellular localization and activity of splice factors. 15 We also identified several substrates of SRPK2 to be aberrantly expressed or phosphorylated in HNSCC cells.…”

Elevated SRPK1 lessens apoptosis in breast cancer cells through RBM4-regulated splicing events

“…An increase in the intracellular level of SRPK1, a major kinase of SR proteins, has been demonstrated to be critical in the regulation of the alternative splicing profile of malignant cells (Gout et al 2012;Odunsi et al 2012;. Mutations of Wilms' tumor suppressor gene (WT1) lead to the up-regulation of SRPK1, which diminishes the SRSF1-mediated up-regulation of VEGF165b (Amin et al 2011).…”

Alternative Splicing in CKD

“…54,55 The lower availability results in alterations in AS of specific genes regulated by MBNL, which contribute to myotonic dystrophy pathogenesis. SRPK1, a kinase that phosphorylates SR-proteins (the class of splice factors mentioned above), is overexpressed in several cancers [56][57][58] and also in DenysDrash syndrome, associated renal failure, and increased incidence of Wilms tumors. 59 SRPK1 is a determinant of angiogenesis through modulation of VEGF-A splicing and its abnormal expression maintains a pathologic loop by promoting proangiogenic and propermeability VEGF-A isoforms.…”