Modulation of cell proliferation by the integrin cytoplasmic domain

Macromolecular crowding regulates matrix composition and gene expression in human gingival fibroblast cultures

Standard cell cultures are performed in aqueous media with a low macromolecule concentration compared to tissue microenvironment. In macromolecular crowding (MMC) experiments, synthetic polymeric crowders are added into cell culture media to better mimic macromolecule concentrations found in vivo. However, their effect on cultured cells is incompletely understood and appears context-dependent. Here we show using human gingival fibroblasts, a cell type associated with fast and scarless wound healing, that MMC (standard medium supplemented with Ficoll 70/400) potently modulates fibroblast phenotype and extracellular matrix (ECM) composition compared to standard culture media (nMMC) over time. MMC significantly reduced cell numbers, but increased accumulation of collagen I, cellular fibronectin, and tenascin C, while suppressing level of SPARC (Secreted Protein Acidic and Cysteine Rich). Out of the 75 wound healing and ECM related genes studied, MMC significantly modulated expression of 25 genes compared to nMMC condition. MMC also suppressed myofibroblast markers and promoted deposition of basement membrane molecules collagen IV, laminin 1, and expression of LAMB3 (Laminin Subunit Beta 3) gene. In cell-derived matrices produced by a novel decellularization protocol, the altered molecular composition of MMC matrices was replicated. Thus, MMC may improve cell culture models for research and provide novel approaches for regenerative therapy.

Integrin expression and IgA nephropathy: in vitro modulation by IgA with altered glycosylation and macromolecular IgA

BACKGROUND

Signal transduction by mesangial cell (MC) integrins regulates cell growth and survival, extracellular matrix production, and organization. The aim of the study was to investigate human MC integrin modulation by differently glycosylated IgA and macromolecular IgA, which are thought to play a pathogenetic role in IgA nephropathy (IgAN).

METHODS

MCs were incubated with purified human polymeric IgA, heat-aggregated IgA, IgA glycoforms generated by enzymatic hydrolysis of saccharide residues and serum fractions from IgAN patients, and controls isolated by lectin affinity and containing IgA with peculiar glycan patterns. Integrins were quantitated by flow cytometry.

RESULTS

Cultured MCs highly expressed alphavbeta3 and some alpha3beta1; alphavbeta3 was up-regulated by matrix components (P < 0.02). In vitro desialylated and degalactosylated polymeric human IgA enhanced alphavbeta3 expression on cultured MCs (P < 0.001). Serum IgA glycoforms isolated from IgAN patients with high exposure of internal sugars, GalNAc, Neu5Ac2,6GalNAc, and Man enhanced alphav expression on cultured MCs more than healthy controls. CONCLUSIONS.: These data support the hypothesis that IgA glycation plays a role in modulating the cell-matrix interaction, and that this mechanism can be operating in IgAN.

Regulation of mRNA and protein levels of beta1 integrin variants in human prostate carcinoma

Alterations of integrin expression levels in cancer cells correlate with changes in invasiveness, tumor progression, and metastatic potential. The beta1C integrin, an alternatively spliced form of the human beta1 integrin, has been shown to inhibit prostate cell proliferation. Furthermore, beta1C protein levels were found to be abundant in normal prostate glandular epithelium and down-regulated in prostatic adenocarcinoma. To gain further insights into the molecular mechanisms underlying abnormal cancer cell proliferation, we have studied beta1C and beta1 integrin expression at both mRNA and protein levels by Northern and immunoblotting analysis using freshly isolated neoplastic and normal human prostate tissue specimens. Steady-state mRNA levels were evaluated in 38 specimens: 33 prostatic adenocarcinomas exhibiting different Gleason's grade and five normal tissue specimens that did not show any histological manifestation of benign prostatic hypertrophy. Our results demonstrate that beta1C mRNA is expressed in normal prostate and is significantly down-regulated in neoplastic prostate specimens. In addition, using a probe that hybridizes with all beta1 variants, mRNA levels of beta1 are found reduced in neoplastic versus normal prostate tissues. We demonstrate that beta1C mRNA down-regulation does not correlate with either tumor grade or differentiation according to Gleason's grade and TNM system evaluation, and that beta1C mRNA levels are not affected by hormonal therapy. In parallel, beta1C protein levels were analyzed. As expected, beta1C is found to be expressed in normal prostate and dramatically reduced in neoplastic prostate tissues; in contrast, using an antibody to beta1 that recognizes all beta1 variants, the levels of beta1 are comparable in normal and neoplastic prostate, thus indicating a selective down-regulation of the beta1C protein in prostate carcinoma. These results demonstrate for the first time that beta1C and beta1 mRNA expression is down-regulated in prostate carcinoma, whereas only beta1C protein levels are reduced. Our data highlight a selective pressure to reduce the expression levels of beta1C, a very efficient inhibitor of cell proliferation, in prostate malignant transformation.

Adhesion complexes implicated in intestinal epithelial cell-matrix interactions

This article review summarizes data on cell-substratum adhesion complexes involved in the regulation of cellular functions in the intestine. We first focus on the molecular composition of the two main adhesion structures-the beta1 integrin-adhesion complex and the hemidesmosome-found in vivo and in two human intestinal cell lines. We also report the key findings on the cellular behavior and response to the extracellular matrix that involve integrins, the main transmembrane anchors of these complexes. How the dynamics of cell/extracellular matrix interactions contribute to cell migration, proliferation, differentiation, and tumorigenicity is discussed in the light of the data provided by the human intestinal cells.

Interaction of the integrin beta1 cytoplasmic domain with ICAP-1 protein

In a yeast two-hybrid screen, a protein named ICAP-1 (beta1 integrin cytoplasmic domain associated protein) associated with the integrin beta1 cytoplasmic tail but not with tails from three other integrin beta subunits (beta2, beta3, and beta5) or from seven different alpha subunits. Likewise in human cells, ICAP-1 associated specifically with the beta1 but not beta2, beta3, or beta5 tails. The carboxyl-terminal 14 amino acids of beta1 were critical for ICAP-1 interaction. ICAP-1 is a ubiquitously expressed protein of 27 and 31 kDa, with the smaller form being preferentially solubilized by Triton X-100. Phosphorylation of both 27- and 31-kDa forms was constitutive but was increased by 1.5-2-fold upon cell spreading on fibronectin, compared with poly-L-lysine. Also, ICAP-1 contributes to beta1 integrin-dependent migration because (i) ICAP-1 transfection markedly increased chemotactic migration of COS7 cells through fibronectin-coated but not vitronectin-coated porous filters, and (ii) support of beta1-dependent cell migration (in Chinese hamster ovary cells transfected with various wild type and mutant beta1 forms) correlated with ICAP-1 association. In summary, ICAP-1 (i) associates specifically with beta1 integrins, (ii) is phosphorylated upon beta1 integrin-mediated adhesion, and (iii) may regulate beta1-dependent cell migration.