Retinoic acid receptor gamma impacts cellular adhesion, Alpha5Beta1 integrin expression and proliferation in K562 cells

Abstract

The interplay between cellular adhesion and proliferation is complex; however, integrins, particularly the α5β1 subset, play a pivotal role in orchestrating critical cellular signals that culminate in cellular adhesion and growth. Retinoids modify the expression of a variety of adhesive/proliferative signaling proteins including α5β1 integrins; however, the role of specific retinoic acid receptors involved in these processes has not been elucidated. In this study, the effect of all-trans-retinoic acid receptor (RAR) agonists on K562 cellular adhesion, proliferation, and α5β1 integrin cell surface expression was investigated. RARγ agonist exposure increased K562 cellular adhesion to RGD containing extracellular matrix proteins fibronectin and FN-120 in a time- and concentration dependent manner, while RARα or RARβ agonist treatment had no effect on cellular adhesion. Due to the novel RARγ- dependent cellular adhesion response exhibited by K562 cells, we examined α5 and β1 integrin subunit expression when K562 cells were exposed to retinoid agonists or vehicle for 24, 48, 72 or 96 hours. Our data demonstrates no differences in K562 cell surface expression of the α5 integrin subunit when cells were exposed to RARα, RARβ, or RARγ agonists for all time points tested. In contrast, RARγ agonist exposure resulted in an increase in cell surface β1 integrin subunit expression within 48 hours that was sustained at 72 and 96 hours. Finally, we demonstrate that while exposure to RARα or RARβ agonists have no effect on K562 cellular proliferation, the RARγ agonist significantly dampens K562 cellular proliferation levels in a time- and concentration- dependent manner. Our study is the first to report that treatment with a RARγ specific agonist augments cellular adhesion to α5β1 integrin substrates, increases cell surface levels of the β1 integrin subunit, and dampens cellular proliferation in a time and concentration dependent manner in a human erythroleukemia cell line.

Evolution from adherent to suspension: systems biology of HEK293 cell line development

“…In addition, lysyl oxidase (LOX), an enzyme responsible for the covalent cross-linking between elastin and collagen in the extracellular matrix, has been shown to be important for cell-matrix adhesion formation, supporting the adherent phenotype of adherent cells but is also associated with cell invasion and induction of EMT 62,63 . Besides the EMT-related genes, the additional three genes (RARG, ZIC1 and DHRS3), consistently up-regulated in adherent cells compared to suspension cell lines, have previously been associated with increased cell adhesion through the retinoic acid signaling pathway [64][65][66][67] . In line with this, retinol metabolism was found to be down-regulated in suspension cells in the metabolic gene set analysis (Fig.…”

Polymeric siRNA delivery targeting integrin-β1 could reduce interactions of leukemic cells with bone marrow microenvironment

“…Other integrins analyzed such as ITGA2B, ITGA3, ITGA10, ITGAE, ITGB3 and ITGB5 had very low or no expression (Figure S1). Given the well-established role of integrin-β1 in fibronectin binding [30] , [31] , [32] , [33] , [34] , this analysis suggests that integrin-β1 could be primarily responsible for the fibronectin binding ability of the K562 cells. A similar level of Integrin-β1 was also observed when K562 cells were cultured in contact with hBMSC (Figure S1, insert)…”

“…Compelling evidences of integrin-β1 as a key molecule that aids in the binding of CML cells to BM/fibronectin, transform them into a viable target to overcome drug resistance. The fact that integrin-β1 mediated pathway was shown to mediate fibronectin binding by various studies [ [31] , [32] , [33] , [34] , 36 ], regulate degradation of Bim pro-apoptotic protein levels [30] , prevent apoptosis in BCR-ABL positive cells [13] , all contributed to our focussing on integrin-β1 as a therapeutic target.…”