Collagen Receptor Control of Epithelial Morphogenesis and Cell Cycle Progression

Abstract

To define the unique contributions of the ␣ subunit cytoplasmic tails of the ␣ 1 ␤ 1 and ␣ 2 ␤ 1 integrin to epithelial differentiation and branching morphogenesis , a variant NMuMG cell line lacking ␣ 1 ␤ 1 and ␣ 2 ␤ 1 integrin expression was stably transfected with the full-length ␣ 2 integrin subunit cDNA (X2C2) , chimeric cDNA consisting of the extracellular and transmembrane domains of the ␣ 2 subunit and the cytoplasmic domain of the ␣ 1 subunit (X2C1) , or ␣ 2 cDNA truncated after the GFFKR sequence (X2C0). The X2C2 and X2C1 transfectants effectively adhered , spread, and formed focal adhesion complexes on type I collagen matrices. The X2C0 transfectants were less adherent to low concentrations of type I collagen , spread less well , and formed poorly defined focal adhesion complexes in comparison to the X2C2 and X2C1 transfectants. The X2C2 and X2C1 transfectants but not the X2C0 transfectants proliferated on collagen substrates. Only the X2C2 transfectants developed elongate branches and tubules in three-dimensional collagen gels and migrated on type I collagen. These findings suggest a unique role for the ␣ 2 integrin cytoplasmic domain in postligand binding events and cooperative interactions with growth factors that mediate epithelial differentiation and branching morphogenesis. Either intact ␣ 1 or ␣ 2 integrin subunit cytoplasmic domain can promote cell cycle progression. (Am J Pathol 1999, 155:927-940)The ␣ 2 ␤ 1 integrin, a collagen/laminin receptor, is expressed at high levels by most normal epithelial cells, and its expression is required for normal epithelial organization, including the formation of branching glands and ducts of the breast. [1][2][3][4][5][6][7][8][9][10] In many epithelial malignancies, ␣ 2 ␤ 1 integrin expression is diminished or lost in a manner that correlates with the loss of epithelial differentiation and tumor progression. 2,3,[11][12][13][14] The important role that the ␣ 2 ␤ 1 integrin plays in normal epithelial differentiation has been substantiated by a number of in vitro "gain-offunction" and "loss-of-function" models. 4,5,15,16 For example, when a full-length ␣ 2 integrin cDNA was introduced into a poorly differentiated, tumorigenic murine breast cancer cell line that expressed no detectable ␣ 2 integrin subunit but high levels of the ␣ 1 integrin subunit, reexpression of the ␣ 2 ␤ 1 integrin resulted in dramatic phenotypic alteration from a fibroblastoid, spindleshaped, non-contact-inhibited cell to an epithelioid, polygonal-shaped, and contact-inhibited cell in culture. 15 Although the adhesion to collagen (mediated by the ␣ 1 ␤ 1 integrin) of the parental and control cells was comparable to the adhesion of the ␣ 2 transfectants, only the ␣ 2 transfectants formed organized structures, including alveolarlike and elongated multilayered duct-like structures in three-dimensional floating collagen gels. These findings suggested that expression of the ␣ 2 ␤ 1 integrin, but not the ␣ 1 ␤ 1 integrin, supported epithelial differentiation and glandular morphogenesis in vi...

Regulation of paxillin family members during epithelial-mesenchymal transformation: a putative role for paxillin δ

“…Thus, as reported in other epithelial cell model systems, a regulated Crk association with paxillin is likely to play a critical role in the regulation of morphology and motility in NMuMG cells. Although the reason for the discrepancy between our own results and the other NMuMG studies is unclear, the difference could be attributed to cell-specific differences as a number of clonal lines exhibiting a variety of phenotypes have been derived from the parental NMuMG population (Soriano et al, 1995;Zutter et al, 1999).…”

Spike Formation by Fibroblasts Adhering to Fibrillar Collagen I Gel

“…Cells respond to collagen I using integrins a1b1, a2b1, and avb3 (Klein et al, 1991;Langholz et al, 1995;Pozzi et al, 1998;Ivaska et al, 1999;Zutter et al, 1999;Kanda et al, 2000;Cooke et al, 2000;Heino, 2000), and DDR2 (Olaso et al, 2002). Skin fibroblasts use a2b1 to adhere onto collagen I (Klein et al, 1991;Langholz et al, 1995;Ivaska et al, 1999).…”

“…Integrin a2b1 is the most important fibrillar collagen receptor for collagen gel contraction via cell-cell contact formation and actin stress fiber formation (Langholz et al, 1995;reviewed by Heino, 2000). The integrin a2 cytoplasmic domain regulates the cell branching morphogenesis and the force development (Zutter et al, 1999). Notably, endothelial cells invade the inside of collagen gels through integrin avb3 which recognizes the RGD motif in fibrillar collagen I (Kuzuya et al, 1999;Kanda et al, 2000).…”

Rapid Prototyping of Engineered Heart Tissues through Miniaturization and Phenotype-Automation

“…We were the first to introduce the use of tissue models to determine effective drug doses [38] and have recently extended the application of this technology to include phenotypic screening [39]. We demonstrated the phenotypic difference in tissue mechanics between wildtype cells and mutant cells with truncated 1 integrin [40]. We also extended the applications of engineered tissue models by creating cardiac tissue constructs [41].…”