The Met Receptor and α6β4 Integrin Can Function Independently to Promote Carcinoma Invasion

Abstract

It has been proposed that a constitutive, physical association of the Met receptor and the ␣ 6 ␤ 4 integrin exists on the surface of invasive carcinoma cells and that hepatocyte growth factor (HGF)-mediated invasion is dependent on ␣ 6 ␤ 4 (Trusolino, L., Bertotti, A., and Comoglio, P. M. (2001) Cell 107, 643-654). The potential significance of these results prompted us to re-examine this hypothesis. Using three different carcinoma cell lines that express both Met and ␣ 6 ␤ 4 , we were unable to detect the constitutive association of these receptors by co-immunoprecipitation. Moreover, carcinoma cells that lacked expression of ␣ 6 ␤ 4 exhibited Met-dependent invasion toward HGF, and increasing Met expression by viral infection of these cells enhanced invasion without inducing ␣ 6 ␤ 4 expression. Although expression of ␣ 6 ␤ 4 in such cells enhanced their invasion to HGF, it also enhanced their ability to invade toward other chemoattractants such as lysophosphatidic acid, and this latter invasion was not inhibited by a function-blocking Met antibody. Finally, depletion of ␤ 4 by RNA interference in invasive carcinoma cells that express both receptors reduced the ability of these cells to invade toward HGF by ϳ25%, but it did not abrogate their invasion. These data argue that the invasive function of Met can be independent of ␣ 6 ␤ 4 and that ␣ 6 ␤ 4 has a generic influence on the invasion of carcinoma cells that is not specific to Met.Understanding the receptor-mediated mechanisms that underlie invasive carcinoma is a timely and significant endeavor. The involvement of specific integrins and growth factor receptors in the invasive process is established, and several lines of evidence indicate that these two classes of surface receptors may cooperate to effect a wide range of biological functions, including the migration and invasion of tumor cells (2-4). The available data indicate that integrin and growth factor signaling can be synergistic, and in some cases physical association may occur between these receptor types. Insight into the nature of such receptor interactions has important implications not only for understanding the biology of tumor invasion but also for the design and use of therapeutics targeted to these receptors (5).

Tetraspanin KAI1/CD82 suppresses invasion by inhibiting integrin-dependent crosstalk with c-Met receptor and Src kinases

“…Previous studies have suggested that c-Met and laminin integrins may interact to regulate invasion (Trusolino et al, 2001;Chung et al, 2004). Our studies found that PC3 cells express higher levels of c-Met relative to DU145 cells and integrins were incapable of activating c-Met in DU145 cells.…”

Upregulation and redistribution of integrin α6β4 expression occurs at an early stage in pancreatic adenocarcinoma progression

“…35,36 c-Met is known to cooperate with integrin a6b4 to enhance the migratory and invasive potential of cancer cells in vitro. 37,38 Furthermore, the tumorigenic potential of c-Met in cancer cells in vitro has been attributed to its cooperation with the integrin a6b4. 39 The integrin a6b4 has also been shown to promote the signaling of transcription factors such as NFAT-1 in carcinoma cells.…”

Loss of β4 Integrin Subunit Reduces the Tumorigenicity of MCF7 Mammary Cells and Causes Apoptosis upon Hormone Deprivation

“…To investigate the loss of function of h 4 integrin signaling, we used RNA interference to block the expression of h 4 subunit as previously described (21). We first analyzed the expression of h 4 integrin subunit upon shRNA interference.…”

“…NIH3T3 cells were maintained in DMEM supplemented with 10% FCS. The inactivation of h 4 was obtained by LipofectAMINE PLUS method (Invitrogen) using pSUPER.retro vector containing h 4 -shRNA or a scramble RNA (scr-shRNA) sequences as previously described (21). Selection of puromycin-positive cells was carried out using 500 Ag/mL puromycin (Sigma, Milan, Italy).…”