CLK2 Is an Oncogenic Kinase and Splicing Regulator in Breast Cancer

Abstract

Genetically activated kinases have been attractive therapeutic targets in cancer due to the relative ease of developing tumorspecific treatment strategies for them. To discover novel putative oncogenic kinases, we identified 26 genes commonly amplified and overexpressed in breast cancer and subjected them to a lentiviral shRNA cell viability screen in a panel of breast cancer cell lines. Here, we report that CLK2, a kinase that phosphorylates SR proteins involved in splicing, acts as an oncogene in breast cancer. Deregulated alternative splicing patterns are commonly observed in human cancers but the underlying mechanisms and functional relevance are still largely unknown. CLK2 is amplified and overexpressed in a significant fraction of breast tumors. Downregulation of CLK2 inhibits breast cancer growth in cell culture and in xenograft models and it enhances cell migration and invasion. Loss of CLK2 in luminal breast cancer cells leads to the upregulation of epithelial-to-mesenchymal transition (EMT)-related genes and a switch to mesenchymal splice variants of several genes, including ENAH (MENA). These results imply that therapeutic targeting of CLK2 may be used to modulate EMT splicing patterns and to inhibit breast tumor growth. Cancer Res; 75(7); 1516-26.Ó2015 AACR.

A triple exon-skipping luciferase reporter assay identifies a new CLK inhibitor pharmacophore

“…22 Using this screening approach we have identified compounds that are dual CLK2/CDK1 inhibitors (such as 1 ) that we optimized to yield more specific CLK inhibitors (such as SRI-29329, 8 ). This is a notable result since CLK2 50 and CDK1 51 have been independently identified as potential targets for breast cancer. Therefore these active analogs, SAR results and our MDM2-Luc assay may facilitate the development of new probe and lead molecules with potential application in breast cancer, and other diseases.…”

CLK-dependent exon recognition and conjoined gene formation revealed with a novel small molecule inhibitor

“…In terms of the potential applications of T3 in disease, previous reports demonstrate that knockdown of CLK2 inhibits growth of breast tumors with overexpresseed CLK2 in cell and animal models of the disease, correlating with splicing alterations 12 . Inhibition of CLK1 by TG003 or KH-CB19 blocks proliferation 13 similar to T3 treatment, suggesting that T3 may be relevant in the treatment of diseases, such as breast and kidney cancers, where respective CLKs are deregulated.…”

“…AS has been implicated in a wide range of diseases, including cancer 5–7 and pre-malignant states such as myelodysplasia 8–11 through mutation of SF3B proteins. Recently, CLK2 has been suggested as an oncogenic kinase in breast cancer 12 and CLK1-regulated AS is deregulated in kidney cancers 13 .…”

RNA splicing factors as oncoproteins and tumour suppressors

“…For example, SR proteins are phosphorylated by kinases including topoisomerase I and members of the SR protein kinase (SRPK) and CDC2-like kinase (CLK) families 159–161 . These kinases affect SR protein subcellular localization and splicing activity 162,163 , exhibit altered expression and/or activity in cancer 164,165 , and can potentially act as oncogenes 165 . Small molecules that block activity of these kinases have been identified, including TG003, an inhibitor of CLK1 and CLK4, and SRPIN340, an SRPK1 and SRPK2 inhibitor that inhibits angiogenesis 166,167 .…”