We studied the expression pattern and the role of CD44 in regulating the malignant behavior of two cholangiocarcinoma (CCA) cell lines which expressed different levels of CD44 using the siRNA technique. KKU-100, the high CD44 expresser, exhibited a high degree of in vitro invasiveness, migration and adhesion to Matrigel compared to HuCCA-1. Silencing of CD44 by siRNA did not have a significant effect on cell proliferation. However, in vitro invasiveness, directional migration (chemotaxis) and adhesion to Matrigel were markedly reduced in both cell lines, although chemokinesis and MMP secretion were variable, demonstrating the distinct functional role and requirement for CD44 in different cellular activities and in different cell types. In addition, immunohistochemical analysis suggested that CD44 may be involved in the differentiation process or tumor progression, depending on the macroscopic type of CCA. Taken together, our data indicate that CD44 is an important requirement for the invasive phenotype of CCA cells, although the role that CD44 plays may vary depending on the CCA type and the cellular activity in which it is engaged.

No abstract

Vba5p is closest to Vba3p in the vacuolar transporter for basic amino acids (VBA) family of Saccharomyces cerevisiae. We found that green fluorescence protein (GFP)-tagged Vba5p localized exclusively to the plasma membrane. The uptake of lysine and arginine by whole cells was little affected by deletion of the VBA5 gene, but was stimulated by overexpression of the VBA5 gene. The inhibitory effect of 4-nitroquinoline N-oxide on cell growth was accelerated by expression of the VBA5 gene, and was lessened by the addition of arginine. These results suggest that Vba5p is a plasma membrane protein involved in amino acid uptake and drug sensitivity.

No abstract

In the vacuolar basic amino acid (VBA) transporter family of Saccharomyces cerevisiae, VBA4 encodes a vacuolar membrane protein with 14 putative transmembrane helices. Transport experiments with isolated vacuolar membrane vesicles and estimation of the amino acid contents in vacuoles showed that Vba4p is not likely involved in the transport of amino acids. We found that the vba4Δ cells, as well as vba1Δ and vba2Δ cells, showed increased susceptibility to several drugs, particularly to azoles. Although disruption of the VBA4 gene did not affect the salt tolerance of the cells, vacuolar fragmentation observed under high salt conditions was less prominent in vba4Δ cells than in wild type, vba1Δ, and vba2Δ cells. Vba4p differs from Vba1p and Vba2p as a vacuolar transporter but is important for the drug resistance and vacuolar morphology of S. cerevisiae.