Pila Estess

Proinflammatory stimuli regulate endothelial hyaluronan expression and CD44/HA-dependent primary adhesion.

The localization of circulating leukocytes within inflamed tissues occurs as the result of interactions with and migration across vascular endothelium, and is governed, in part, by the expression of adhesion molecules on both cell types. Recently, we have described a novel primary adhesion interaction between the structurally activated form of the adhesion molecule CD44 on lymphocytes and its major ligand hyaluronan on endothelial cells under physiologic laminar flow conditions, and have proposed that this interaction functions in an extravasation pathway for lymphocytes in vascular beds at sites of inflammation. While the regulation of activated CD44 on leukocytes has been characterized in depth, regulation of hyaluronate (HA) on endothelial cells has not been extensively studied. Here we demonstrate that the expression of HA on cultured endothelial cell lines and primary endothelial cultures is inducible by the proinflammatory cytokines TNFalpha and IL-1beta, as well as bacterial lipopolysaccharide. In addition, this inducibility appears strikingly restricted to endothelial cells derived from microvascular, but not large vessel, sources. The elevated HA levels thus induced result in increased CD44-dependent adhesive interactions in both nonstatic shear and laminar flow adhesion assays. Changes in mRNA levels for the described HA synthetic and degradative enzymes were not found, suggesting other more complex mechanisms of regulation. Together, these data add to the selectin and immunoglobulin gene families a new inducible endothelial adhesive molecule, hyaluronan, and help to further our understanding of the potential physiologic roles of the CD44/HA interaction; i.e., local cytokine production within inflamed vascular beds may enhance surface hyaluronan expression on endothelial cells, thereby creating local sites receptive to the CD44/HA interaction and thus extravasation of inflammatory cells.

Activation and interaction of CD44 and hyaluronan in immunological systems

Adhesive interactions between receptors on vascular endothelial cells (EC) and circulating leukocytes are pivotal in regulating leukocyte extravasation. Although primary adhesion of lymphocytes to EC has been primarily attributed to the selectin family of receptors, CD44 can also mediate this function when activated to bind its ligand hyaluronan (HA). Triggering through the T cell receptor induces activated CD44 and CD44‐dependent primary adhesion in both human and mouse lymphocytes, and the interaction can mediate the extravasation of activated T cells into an inflamed site. Lymphocytes capable of CD44/HA‐dependent primary adhesion are found in peripheral blood of some rheumatologic patients, and their presence is associated with concurrent symptomatic or active disease. Thus, circulating T cells bearing activated CD44 may represent a pathogenically important subpopulation of activated cells that is elevated under conditions of chronic inflammation. Together, these data add to the selectin and immunoglobulin gene families a new receptor/ligand pair and further our understanding of their potential physiological role; i.e., antigen‐specific T cell activation together with local vascular inflammation permits the CD44/HA interaction and subsequent T cell extravasation. J. Leukoc. Biol. 66: 315–321; 1999.

Bimolecular Complex between Rolling and Firm Adhesion Receptors Required for Cell Arrest: CD44 Association with VLA-4 in T Cell Extravasation

CD44 on activated T cells can initiate contact and mediate rolling on hyaluronan on endothelial cells. We have shown that the integrin VLA-4 is used preferentially over LFA-1 in conjunction with this rolling interaction for firm adhesion. Here, we show by coimmunoprecipitation and transfection studies that CD44 associates with VLA-4 but not LFA-1 on the plasma membrane of immune cells. Absence of the cytoplasmic portion of CD44 abrogates this coassociation and attendant firm adhesion. Moreover, in an in vivo model of lymphocyte homing, cells expressing only the truncated form of CD44 together with VLA-4 fail to traffic to an inflamed site, thereby defining a discrete biological role for the cytoplasmic domain. These studies demonstrate a molecular mechanism whereby coanchoring within a single bimolecular complex between a primary and secondary adhesion molecule regulates a cells ability to firmly adhere, providing a fundamental alteration to the paradigm of leukocyte extravasation.

Polymorphisms, mutations, and amplification of the EGFR gene in non-small cell lung cancers

Background The epidermal growth factor receptor (EGFR) gene is the prototype member of the type I receptor tyrosine kinase (TK) family and plays a pivotal role in cell proliferation and differentiation. There are three well described polymorphisms that are associated with increased protein production in experimental systems: a polymorphic dinucleotide repeat (CA simple sequence repeat 1 [CA-SSR1]) in intron one (lower number of repeats) and two single nucleotide polymorphisms (SNPs) in the promoter region, −216 (G/T or T/T) and −191 (C/A or A/A). The objective of this study was to examine distributions of these three polymorphisms and their relationships to each other and to EGFR gene mutations and allelic imbalance (AI) in non-small cell lung cancers. Methods and Findings We examined the frequencies of the three polymorphisms of EGFR in 556 resected lung cancers and corresponding non-malignant lung tissues from 336 East Asians, 213 individuals of Northern European descent, and seven of other ethnicities. We also studied the EGFR gene in 93 corresponding non-malignant lung tissue samples from European-descent patients from Italy and in peripheral blood mononuclear cells from 250 normal healthy US individuals enrolled in epidemiological studies including individuals of European descent, African–Americans, and Mexican–Americans. We sequenced the four exons (18–21) of the TK domain known to harbor activating mutations in tumors and examined the status of the CA-SSR1 alleles (presence of heterozygosity, repeat number of the alleles, and relative amplification of one allele) and allele-specific amplification of mutant tumors as determined by a standardized semiautomated method of microsatellite analysis. Variant forms of SNP −216 (G/T or T/T) and SNP −191 (C/A or A/A) (associated with higher protein production in experimental systems) were less frequent in East Asians than in individuals of other ethnicities (p < 0.001). Both alleles of CA-SSR1 were significantly longer in East Asians than in individuals of other ethnicities (p < 0.001). Expression studies using bronchial epithelial cultures demonstrated a trend towards increased mRNA expression in cultures having the variant SNP −216 G/T or T/T genotypes. Monoallelic amplification of the CA-SSR1 locus was present in 30.6% of the informative cases and occurred more often in individuals of East Asian ethnicity. AI was present in 44.4% (95% confidence interval: 34.1%–54.7%) of mutant tumors compared with 25.9% (20.6%–31.2%) of wild-type tumors (p = 0.002). The shorter allele in tumors with AI in East Asian individuals was selectively amplified (shorter allele dominant) more often in mutant tumors (75.0%, 61.6%–88.4%) than in wild-type tumors (43.5%, 31.8%–55.2%, p = 0.003). In addition, there was a strong positive association between AI ratios of CA-SSR1 alleles and AI of mutant alleles. Conclusions The three polymorphisms associated with increased EGFR protein production (shorter CA-SSR1 length and variant forms of SNPs −216 and −191) were found to be rare in East Asians as compared to other ethnicities, suggesting that the cells of East Asians may make relatively less intrinsic EGFR protein. Interestingly, especially in tumors from patients of East Asian ethnicity, EGFR mutations were found to favor the shorter allele of CA-SSR1, and selective amplification of the shorter allele of CA-SSR1 occurred frequently in tumors harboring a mutation. These distinct molecular events targeting the same allele would both be predicted to result in greater EGFR protein production and/or activity. Our findings may help explain to some of the ethnic differences observed in mutational frequencies and responses to TK inhibitors.