The alpha6beta4 integrin maintains the survival of human breast carcinoma cells in vivo.
The alpha6beta4 integrin has been widely implicated in carcinoma function in vitro; however, in vivo data are scarce. To determine the importance of alpha6beta4 in tumor progression, a SUM-159 breast carcinoma cell line that is essentially devoid of alpha6beta4 expression was generated using an RNA interference strategy. Loss of alpha6beta4 expression inhibits colony formation in soft agar assays, suggesting a vital role for alpha6beta4 in survival signaling and anchorage-independent growth. Orthotopic injection of the beta4-deficient cell line into the mammary fat pad of immunocompromised mice yielded significantly fewer and smaller tumors than the control cell line, revealing a role for the alpha6beta4 integrin in tumor formation. Under conditions that mimicked the in vivo environment, decreased expression of the alpha6beta4 integrin led to enhanced apoptosis as determined by the percentage of Annexin V-FITC+, PI- cells and the presence of caspase-3 cleavage products. Recombinant vascular endothelial growth factor (VEGF) significantly inhibited the cell death observed in the beta4-deficient cell line, demonstrating the importance of VEGF expression in this survival pathway. Furthermore, loss of alpha6beta4 expression leads to enhanced apoptosis and reduced expression of VEGF in breast carcinoma cells in vivo. Importantly, the specificity of alpha6beta4 in both the in vitro and in vivo assays showed that reexpression of the beta4 subunit into the beta4-deficient cell line could rescue the functional phenotype. Taken together, these data implicate the alpha6beta4 integrin in tumor formation by regulating tumor cell survival in a VEGF-dependent manner.
Lipscomb
Elizabeth A
EA
Division of Cancer Biology and Angiogenesis, Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Simpson
Kaylene J
KJ
Lyle
Stephen R
SR
Ring
Jennifer E
JE
Dugan
Aisling S
AS
Mercurio
Arthur M
AM
D017209:Apoptosis / Q000502:physiology; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D006801:Humans; D039161:Integrin alpha6beta4 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D039663:Integrin beta4 / Q000235:genetics; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis
D039161:Integrin alpha6beta4; D039663:Integrin beta4; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D042461:Vascular Endothelial Growth Factor A