ABSTRACT
Megakaryoblastic Leukemia 1 and 2 (MKL1/2) are transcriptional coactivators of Serum Response Factor (SRF) with an essential role for hepatocellular carcinoma (HCC) growth and oncogene-induced senescence. In this report, we identified myoferlin as a novel MKL/SRF target gene by gene expression profiling and verification in vivo in HCC xenografts. Myoferlin was overexpressed in human and murine HCCs triggered by conditional expression of constitutively active SRF-VP16 protein in hepatocytes. Furthermore, myoferlin was required for HCC cell invasion, proliferation and anchorage-independent cell growth. We provide evidence that myoferlin is a crucial gene target of MKL1/2 mediating its effect on oncogene-induced senescence by modulating the activation state of the EGFR and downstream MAPK and p16-/Rb pathways. Depletion of myoferlin in tumour cells from SRF-VP16-derived murine HCCs induced a senescence phenotype. These findings identify MKL1/2 and myoferlin as novel therapeutic targets to treat human HCC by a senescence-inducing strategy.
Subject(s)
Calcium-Binding Proteins/metabolism , Carcinoma, Hepatocellular/metabolism , Gene Expression Profiling/methods , Liver Neoplasms/metabolism , Membrane Proteins/metabolism , Muscle Proteins/metabolism , Serum Response Factor/metabolism , Trans-Activators/metabolism , Transcription Factors/metabolism , Animals , Calcium-Binding Proteins/genetics , Carcinoma, Hepatocellular/genetics , Cell Line, Tumor , Cell Proliferation , Gene Expression Regulation, Neoplastic , Humans , Liver Neoplasms/genetics , Membrane Proteins/genetics , Mice , Muscle Proteins/genetics , NIH 3T3 Cells , Neoplasm Invasiveness , Neoplasm TransplantationABSTRACT
Deleted in Liver Cancer 1 (DLC1) is a tumor suppressor whose allele is lost in 50% of liver, breast, lung and 70% of colon cancers. Here, we show that the transcriptional coactivators Megakaryoblastic Leukemia 1 and 2 (MKL1/2) are constitutively localized to the nucleus in hepatocellular and mammary carcinoma cells that lack DLC1. Moreover, DLC1 loss and MKL1 nuclear localization correlate in primary human hepatocellular carcinoma. Nuclear accumulation of MKL1 in DLC1-deficient cancer cells is accomplished by activation of the RhoA/actin signaling pathway and concomitant impairment of MKL1 phosphorylation, which results in constitutive activation of MKL1/2 target genes. We provide evidence that MKL1/2 mediates cancerous transformation in DLC1-deficient hepatocellular and mammary carcinoma cells. Depletion of MKL1/2 suppresses cell migration, cell proliferation and anchorage-independent cell growth induced by DLC1 loss.
