The primacy of ?1 integrin activation in the metastatic cascade.

ABSTRACT: After neoplastic cells leave the primary tumor and circulate, they may extravasate from the vasculature and colonize tissues to form metastases. ?1 integrins play diverse roles in tumorigenesis and tumor progression, including extravasation. In blood cells, activation of ?1 integrins can be regulated by "inside-out" signals leading to extravasation from the circulation into tissues. However, a role for inside-out ?1 activation in tumor cell metastasis is uncertain. Here we show that ?1 integrin activation promotes tumor metastasis and that activated ?1 integrin may serve as a biomarker of metastatic human melanoma. To determine whether ?1 integrin activation can influence tumor cell metastasis, the ?1 integrin subunit in melanoma and breast cancer cell lines was stably knocked down with shRNA and replaced with wild-type or constitutively-active ?1. When tumor cells expressing constitutively-active ?1 integrins were injected intravenously into chick embryos or mice, they demonstrated increased colonization of the liver when compared to cells expressing wild-type ?1 integrins. Rescue expression with mutant ?1 integrins revealed that tumor cell extravasation and hepatic colonization required extracellular ligand binding to ?1 as well as ?1 interaction with talin, an intracellular mediator of integrin activation by the Rap1 GTPase. Furthermore, shRNA-mediated knock down of talin reduced hepatic colonization by tumor cells expressing wild-type ?1, but not constitutively-active ?1. Overexpression in tumor cells of the tumor suppressor, Rap1GAP, inhibited Rap1 and ?1 integrin activation as well as hepatic colonization. Using an antibody that detects activated ?1 integrin, we found higher levels of activated ?1 integrins in human metastatic melanomas compared to primary melanomas, suggesting that activated ?1 integrin may serve as a biomarker of invasive tumor cells. Altogether, these studies establish that inside-out activation of ?1 integrins promotes tumor cell extravasation and colonization, suggesting diagnostic and therapeutic approaches for targeting of ?1 integrin signaling in neoplasia.

SUBMITTER: Kato H 

PROVIDER: S-EPMC3463578 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature