αA-Crystallin associates with α6 integrin receptor complexes and regulates cellular signaling

Abstract

Abstractα-crystallins are small heat-shock proteins important to lens transparency that provide the lens with its refractive properties. In their role as molecular chaperones, these crystallins also prevent protein aggregation, affect cytoskeletal remodeling, enhance resistance to cell stress, and provide lens cells with protection against apoptosis. While many of the functions assigned to αA-crystallin are attributable to its presence in the cytoplasm of lens cells, αA-crystallin also has been detected at the lens plasma membrane. However, how αA-crystallin becomes linked to the plasma membrane or what its functions are at this site has remained unknown. In this study, we examined the mechanisms by which αA-crystallin becomes associated with the lens membrane, focusing specifically on its interaction with membrane receptors, and the differentiation-specificity of these interactions. We also determined how the long-term absence of αA-crystallin alters receptor-linked signaling pathways. αA-crystallin association with membrane receptors was determined by coimmunoprecipitation analysis; its membrane localization was examined by confocal imaging; and the effect of αA-crystallin loss-of-function on the activation state of signaling molecules in pathways linked to membrane receptors was determined by immunoblot analysis. The results show that, in lens epithelial cells, plasma membrane αA-crystallin was primarily localized to apicolateral borders, reflecting the association of αA-crystallin with E-cadherin complexes. These studies also provide the first evidence that αA-crystallin maintained its association with the plasma membrane in lens cortical fiber cells, where it was localized to lateral interfaces, and further show that this association was mediated, in part, by αA-crystallin interaction with α6 integrin receptor complexes. We report that the absence of αA-crystallin led to constitutive activation of the stress kinases p38 and JNK, classical inducers of apoptotic cell death, and the loss of the phospho-Bad pro-survival signal, effects that were greatest in differentiating lens fiber cells. Concurrent with this, activation of FAK and ERK kinases was increased, demonstrating that these receptor-linked pathways also were dysregulated in the absence of αA-crystallin. These data link αA-crystallin plasma membrane association to its differentiation-state-specific interaction with E-cadherin and α6 integrin receptor complexes. The changes in cell signaling in αA-crystallin-null lenses suggest that dysregulation of receptor-linked cell-signaling pathways that accompany the failure of αA-crystallin to associate with membrane Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discover...

α6 Integrin Transactivates Insulin-like Growth Factor Receptor-1 (IGF-1R) to Regulate Caspase-3-mediated Lens Epithelial Cell Differentiation Initiation

“…Apoptotic cell death has been reported in developing lenses of ␣A/␣B crystallin double knock-out mice, and associated with the induction of high levels of caspase-3 (80). Interestingly, we found that ␣A-crystallin associates with ␣6 integrin receptor complexes in regions of active lens cell differentiation (81). Furthermore, activation of ␣6 integrin following exposure to PMA induced recruitment of ␣A-crystallin to ␣6 integrin receptor complexes, providing evidence of a direct signaling connection between ␣6 integrin and ␣A-crystallin (81).…”

Integrin linked kinase (ILK) is required for lens epithelial cell survival, proliferation and differentiation

“…The intracellular signalling mediators for integrin signalling, such as focal adhesion kinase (FAK) (Kokkinos et al, 2007) and ILK (Cammas et al, 2012;de Iongh et al, 2005;Weaver et al, 2007) are expressed in the lens and there are indications that these molecules have altered activity in some cataracts (Menko and Andley;Weaver et al, 2008). Moreover, recent studies using the nestin-Cre and Le-Cre lines have demonstrated a requirement of ILK for cell survival and matrix deposition during lens development (Cammas et al, 2012;Samuelsson et al, 2007).…”

ROCKing regeneration: Rho kinase inhibition as molecular target for neurorestoration

“…Thus, pro-regenerative effects of crystallins may, at least partially, be attributed to the regulation of the RhoA/ROCK/cofilin pathway (Wang et al, 2011 ). Because α-crystallin interacts with α6-integrin membrane receptor complexes and alters their cellular signaling (Menko and Andley, 2010 ) a speculative link to RhoA consists in the prevention of the GDP to GTP exchange of RhoA through integrin membrane complex binding of guanine nucleotide exchange factors (Wettschureck and Offermanns, 2002 ).…”