Expression and cellular distribution of alpha(v) integrins in beta(1) integrin-deficient embryonic stem cell-derived cardiac cells

beta (1) integrin-deficient (beta (1) (-/-)) ES cells showed increased diff erentiation of cardiac cells characterized by reduced adhesion and high bea ting frequency. Whereas in whole embryoid body outgrowths of beta (-/-)(1) cells maximum levels of alpha (w), beta (3), and beta (5), integrin mRNA we re delayed and transiently upregulated, in cardiac clusters isolated from b eta (-/-)(1) cells, only beta (3) intesrin mRNA levels were enhanced in com parison to wild-type (wt) cells. To answer the question, whether alpha (v) and beta (3) integrins may compensate, at least partially. the loss of beta (3), integrin function during cardiac differentiation, the distribution of alpha (v) and beta (3), integrins in beta (-/-)(1) and wt pacemaker-like c ardiac cells was analyzed. A different distribution of alpha (v) and beta ( 3), integrins in beta (-/-)(1) v wt cardiac cells was found. In wt cardiac cells, beta (1) integrin was localized in specialized subsarcolemmal region s, in particular, at focal contacts and costameres, but alpha (v) integrin was diffusely distributed. In contrast, in beta (-/-)(1) cardiac cells, alp ha (v) integrin was preponderantly localized at cell membranes, focal conta cts and costameres. beta (3), integrin displayed a diffuse pattern both in wt and in beta (-/-)(1) pacemaker-like cells at early differentiation stage s, whereas at terminal stages. beta (3), was colocalized with sarcomeres in wt, but not in beta (-/-)(1) pacemaker-like cells. Quantitative immunofluo rescence analysis revealed increased alpha (v) and beta (3) integrin levels in beta (-/-)(1) pacemaker-like cardiac cells. Our results led us to concl ude that altered cellular distribution of alpha (v) integrin and upregulati on of beta (3), integrin correlate with growth and survival of beta (-/-)(1 ) cardiac pacemaker-like cells at an early developmental state. However, al pha (v) and beta (3) integrins cannot Functionally compensate the loss of b eta (1), integrin during terminal differentiation of cardiac cells implicat ing that cardiomyocytes require specific beta (1) integrin functions for ca rdiac specialization. (C) 2001 Academic Press.