Integrin α2β1 inhibits MST1 kinase phosphorylation and activates Yes-associated protein oncogenic signaling in hepatocellular carcinoma.

Angela M. Liu,Wanjin Hong,Zhi Xu,John M. Luk,Kwong-Fai Wong

doi:10.18632/oncotarget.12760

Abstract

The Hippo pathway regulates the down-stream target Yes-associated protein (YAP) to maintain organ homeostasis, which is commonly inactivated in many types of cancers. However, how cell adhesion dysregulates the Hippo pathway activating YAP oncogene in hepatocellular carcinoma (HCC) remains unclear. Our findings demonstrate that α2β1 integrin (but not other β1 integrins) expressed in HCC cells, after binding to collagen extracellular matrix, could inhibit MST1 kinase phosphorylation and activate YAP pro-oncogenic activities. Knockdown of integrin α2 gene (ITGA2) suppressed YAP targeted gene expression in vitro. α2β1 and collagen binding resulted in suppressing Hippo signaling of mammalian sterile 20-like kinase 1 (MST1) and Large tumor suppressor homolog 1 (LATS1) with concomitant activation of YAP-mediated connective tissue growth factor (CTGF) gene expression. In vitro kinase assay showed that MST1 is an immediate downstream target of integrin α2 with S1180 residue as the critical phosphorylation site. Clinical correlational analysis using a gene expression dataset of 228 HCC tumors revealed that ITGA2 expression was significantly associated with tumor progression, and co-expression with YAP targeted genes (AXL receptor tyrosine kinase, CTGF, cyclin D1, glypican 3, insulin like growth factor 1 receptor, and SRY-box 4) correlated with survivals of HCC patients. In conclusion, α2β1 integrin activation through cellular adhesion impacts the Hippo pathway in solid tumors and modulates MST1-YAP signaling cascade. Targeting integrin α2 holds promises for treating YAP-positive HCC.

Highlights

Hepatocellular carcinoma (HCC) is a common cancer worldwide with over 700,000 new incidences per year [1, 2], and the major risk factor is associated with chronic hepatitis B infection [3]
To determine which member is involved in regulating the Hippo pathway in hepatocellular carcinoma (HCC), we knocked down each individual subunit gene, and studied the changes in gene expression mediated by Yes-associated protein (YAP) activation in HCC cells [30, 31]
We investigated whether integrin α2 would sustain the expression of YAP targeted genes by modulating the Hippo core kinases mammalian sterile 20-like kinase 1 (MST1) and Large tumor suppressor homolog 1 (LATS1) [32]

Summary

Introduction

Hepatocellular carcinoma (HCC) is a common cancer worldwide with over 700,000 new incidences per year [1, 2], and the major risk factor is associated with chronic hepatitis B infection [3]. Unlike that binding to extracellular matrix, cell-cell interaction activates MST1/2 thereby phosphorylating LATS1/2 using SAV1 as a cofactor. During cell proliferation or organ regeneration (for instance, after partial hepatectomy) the Hippo pathway is inactivated, unleashing YAP and/or TAZ proteins for translocation into the nucleus, where YAP/TAZ protein interacts with transcriptional factors such as TEADs to “switch on” a wide range of genes involved in cell proliferation, dedifferentiation, and survival [12]. In cancer cells the Hippo pathway is inactivated, allowing nuclear YAP/TAZ to modulate genes for metastasis [13,14,15,16]. Our previous study on HCC clinical samples revealed aberrant nuclear YAP expression associated with the poor survival outcomes [17]. Recent study showed a cyclic-YAP peptide that disrupts YAP/TEAD interaction could inhibit HCC cell growth and survival [18]

Methods

Results

Conclusion