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
GlnR plays a major role in regulation in Bacillus subtilis by directly controlling expression of glutamine synthetase (GS) as well as several genes involved in nitrogen metabolism. A GlnR homolog from Staphylococcus aureus was found to complement a B. subtilis glnR mutant, regulating GS levels and glnRA expression in a nitrogen-dependent manner. In a GS null mutant, S. aureus GlnR was not able to influence glnRA transcription, indicating that the S. aureus protein is able to respond to the same signals as its B. subtilis counterpart. This is the first demonstration of a relationship between GS and GlnR from a heterologous system and suggests the presence of a regulatory network in S. aureus that responds to changes in environmental nitrogen similar to that described for B. subtilis.
