Transforming Growth Factor-β Receptor Inhibition Enhances Adenoviral Infectability of Carcinoma Cells via Up-Regulation of Coxsackie and Adenovirus Receptor in Conjunction with Reversal of Epithelial-Mesenchymal Transition

Abstract

Expression of the Coxsackie and Adenovirus Receptor (CAR) is frequently reduced in carcinomas, resulting in decreased susceptibility of such tumors to infection with therapeutic adenoviruses. Because CAR participates physiologically in the formation of tight-junction protein complexes, we examined whether molecular mechanisms known to down-regulate cellcell adhesions cause loss of CAR expression. Transforming growth factor-B (TGF-B)-mediated epithelial-mesenchymal transition (EMT) is a phenomenon associated with tumor progression that is characterized by loss of epithelial-type cell-cell adhesion molecules (including E-cadherin and the tight junction protein ZO-1), gain of mesenchymal biochemical markers, such as fibronectin, and acquisition of a spindle cell phenotype. CAR expression is reduced in tumor cells that have undergone EMT in response to TGF-B. This downregulation results from repression of CAR gene transcription, whereas altered RNA stability and increased proteasomal protein degradation play no role. Loss of CAR expression in response to TGF-B is accompanied by reduced susceptibility to adenovirus infection. Indeed, treatment of carcinoma cells with LY2109761, a specific pharmacologic inhibitor of TGF-B receptor types I and II kinases, resulted in increased CAR RNA and protein levels as well as improved infectability with adenovirus. This was observed in cells induced to undergo EMT by addition of exogenous TGF-B and in those that were transformed by endogenous autocrine/paracrine TGF-B. These findings show down-regulation of CAR in the context of EMT and suggest that combination of therapeutic adenoviruses and TGF-B receptor inhibitors could be an efficient anticancer strategy. (Cancer Res 2006; 66(3): 1648-57)

Blocking transforming growth factor–beta up-regulates E-cadherin and reduces migration and invasion of hepatocellular carcinoma cells

“…Similar results have recently been reported by others, who showed that LY2109761 induces the expression of the Coxachie and adenovirus receptor (CAR), a part of the tight-junction protein complexes involved in the EMT process. 22 This is also consistent with our previous work, in which TGF-␤1 stimulated a more invasive and aggressive phenotype of constitutively noninvasive HCC cells, promoting the EMT via down-regulation of E-cadherin. 10 E-cadherin is a cell-cell adhesion molecule strongly implicated in the invasiveness of different malignancies including HCC, and down-regulation of this molecule has been proposed to have a role in facilitating tumor recurrence and progression.…”

Coxsackie and adenovirus receptor (CAR) is a product of Sertoli and germ cells in rat testes which is localized at the Sertoli–Sertoli and Sertoli–germ cell interface

“…Inflammatory cytokines, such as TNFα, TGFβ and IFNγ, are known to compromise epithelial integrity by repressing cell-cell adhesion molecules (e.g. E-cadherin, ZO-1 and CAR) [36][37][38]. Reduced expression of CAR or E-cadherin was most evident among carcinomas under progression, which was frequently accompanied by cytokine response in vivo [39,40].…”

Expression of the coxsackievirus- and adenovirus receptor in gastrointestinal cancer correlates with tumor differentiation

“…22,23 While the exact molecular mechanisms leading to loss of CAR expression remain unclear, data from others and our laboratory suggest mechanisms underlying loss of CAR expression, such as promoter hypermethylation and repression through activation of Raf-MEK-ERK and TGFb signaling. [24][25][26][27][28] Thus, pharmacological receptor restoration using inhibitors of these pathways may increase the efficiency of adenovirus agents in vivo. 25,27 An alternative route to overcome CARdependent intrinsic resistance to adenovirus infection has been developed that is based on modifying adenovirus capsid proteins in order to retarget the virus to other receptors that are more consistently expressed on cancer cells.…”