Abstract. The integrin ~6/34 is a heterodimer predominantly expressed by epithelia. While no definite receptor function has yet been assigned to it, this integrin may mediate adhesive and/or migratory functions of epithelial cells. We have determined the complete primary structure of both the as and/34 subunits from cDNA clones isolated from pancreatic carcinoma cell line libraries. The deduced amino acid sequence of or6 is homologous to other integrin o~ chains (18-26% identity). Antibodies to an a6 carboxy terminus peptide immunoprecipitated 0t6~4 complexes from carcinoma cells and 0t6/31 complexes from platelets, providing further evidence for the association of ~6 with more than one t3 subunit. The deduced amino acid sequence of/34 predicts an extracellular portion homologous to other integrin/3 chains, and a unique cytoplasmic domain comprised of > 1,000 residues. This agrees with the structures of the ~4 cDNAs from normal epithelial cells (Suzuki, S., and Y. Naitoh. 1990. Organ.] J. 9:765-770). Compared to these structures, however, the /~4 cDNAs that we have cloned from carcinoma cells contain extra sequences. One of these is located in the 5'-untranslated region, and may encode regulatory sequences. Another specifies a segment of 70 amino acids in the cytoplasmic tail. Amplification by reverse transcription-polymerase chain reaction of mRNA indicated that multiple forms of ~4 may exist, possibly due to cell-type specific alternative splicing. The unique structure of/34 suggests its involvement in novel cytoskeletal interactions. Consistent with this possibility, 0t6~4 is mostly concentrated on the basal surface of epithelial cells, but does not colocalize with components of adhesion plaques. EMBO

Enhancement of epithelial cell attachment to laminin-5-coated titanium alloy (Ti-6Al-4V) implant material was evaluated in vitro. Protein analysis showed that Ti6Al-4V has a high affinity for laminin-5 and adsorbed significantly more laminin-5 than laminin-1. DNA analysis showed that laminin-5 enhanced attachment of normal human epidermal keratinocytes (NHEK) to Ti-6Al-4V significantly more than did laminin-1 or uncoated controls. The effect of passivation on laminin-5 adsorption and activity on Ti-6Al-4V also was evaluated. Passivation had no significant effect on the amount of protein adsorbed; however, AFM, ESCA, and ToF-SIMS analyses suggested that passivation affects the conformation of adsorbed laminin-5. Although laminin-5 coating significantly enhanced rapid attachment of epithelial cells to both passivated and unpassivated Ti6Al-4V, surface area measurements showed that cells spread on laminin-5-coated passivated Ti-6Al-4V covered a significantly larger surface area than cells spread on laminin-5-coated unpassivated samples. TEM analysis showed that cells formed significantly more hemidesmosomes on the surface of laminin-5 coated passivated than on the surface of laminin-5 coated unpassivated titanium alloy. The enhancement of rapid cell attachment, spreading, and hemidesmosome assembly on laminin-5-coated passivated samples may reflect better integration between epithelial cells and titanium alloy and thus may be predictive of long-term implant stability.

Pentachlorophenol (PCP) induced expression of the NalC repressor-regulated PA3720- armR operon and the MexR repressor-controlled mexAB-oprM multidrug efflux operon of Pseudomonas aeruginosa . PCP's induction of PA3720- armR resulted from its direct modulation of NalC, the repressor's binding to PA3720- armR promoter-containing DNA as seen in electromobility shift assays (EMSAs) being obviated in the presence of this agent. The NalC binding site was localized to an inverted repeat (IR) sequence upstream of PA3720- armR and overlapping a promoter region whose transcription start site was mapped. While modulation of MexR by the ArmR anti-repressor explains the upregulation of mexAB-oprM in nalC mutants hyperexpressing PA3720- armR , the induction of mexAB-oprM expression by PCP is not wholly explainable by PCP induction of PA3720- armR and subsequent ArmR modulation of MexR, inasmuch as armR deletion mutants still showed PCP-inducible mexAB-oprM expression. PCP failed, however, to induce mexAB-oprM in a mexR deletion strain, indicating that MexR was required for this, although PCP did not modulate MexR binding to mexAB-oprM promoter-containing DNA in vitro . One possibility is that MexR responds to PCP-generated in vivo effector molecules in controlling mexAB-oprM expression in response to PCP. PCP is an unlikely effector and substrate for NalC and MexAB-OprM - its impact on NalC binding to the PA3720- armR promoter DNA occurred only at high µM levels - suggesting that it mimics an intended phenolic effector/substrate(s). In this regard, plants are an abundant source of phenolic antimicrobial compounds and, so, MexAB-OprM may function to protect P. aeruginosa from plant antimicrobials that it encounters in nature.

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