CLIC4, an Intracellular Chloride Channel Protein, Is a Novel Molecular Target for Cancer Therapy

Chloride intracellular channel (CLIC)4 is a p53- and tumor necrosis factor α (TNFα)-regulated chloride channel protein that is localized to the mitochondria and cytoplasm of mouse and human keratinocytes. CLIC4 protein increases in differentiating keratinocytes and in keratinocytes exposed to DNA-damaging agents and metabolic inhibitors. Increasing CLIC4 levels by transduction of recombinant CLIC4 causes apoptosis. CLIC4 translocates to the nucleus under a variety of conditions of cell stress, and nuclear CLIC4 is associated with cell cycle arrest and accelerated apoptosis. Reduction of CLIC4 and several other CLIC family members by expressing a doxycycline-regulated CLIC4 antisense also causes apoptosis in squamous cancer cell lines. Expressing antisense CLIC4 in tumors derived from transplanting these cells into nude mice inhibits tumor growth, increases tumor apoptosis, and reduces tumor cell proliferation. Co-administration of TNFα intraperitoneally enhances the tumor-inhibitory influence of CLIC4 antisense expression. Together, these results suggest that CLIC4 is important for keratinocyte viability and may be a novel target for anti-cancer therapy

Cross-talk between epidermal growth factor receptor and protein kinase C during calcium-induced differentiation of keratinocytes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74029/1/j.1600-0625.2000.009003192.x.pd

Short-Term Retinoic Acid Treatment Increases In Vivo, but Decreases In Vitro, Epidermal Transglutaminase-K Enzyme Activity and Immunoreactivity

Epidermal transglutaminase-K is believed to catalyze the covalent linking of loricrin and involucrin to form cross-linked (CE) envelopes. In normal skin, transglutaminase-K is expressed as a band immediately below the stratum corneum, whereas in psoriasis and healing skin its expression is considerably expanded throughout the suprabasal layers. We have investigated whether the hyperproliferative state induced by short-term application of topical retinoic acid is similarly characterized by an increase in transglutaminase-K enzyme activity and immunoreactivity.Retinoic acid (0.1% cream) or vehicle were applied to human skin and occluded for 4 d. Skin biopsies were obtained for measurement of transglutaminase-K and transglutaminase-C activity and immunoreactivity. For comparison, cultured normal human keratinocytes were incubated for 4 d in the presence of 1 μM retinoic acid and the subsequent transglutaminase-K activity and immunoreactivity measured. Transglutaminase-K activity was increased 2.8 times in retinoic acid compared to vehicle-treated skin (p < 0.005, n = 12) whereas there was no significant difference in transglutaminase-C activity. However, transglutaminase-K mRNA levels were not significantly different between retinoic acid- and vehicle-treated skin. In vehicle-treated skin, transglutaminase-K immunoreactivity was limited to a narrow, substratum corneal band, but was considerably expanded in a diffuse suprabasal pattern in retinoic acid-treated epidermis. In contrast, transglutaminase-K immunostaining was decreased and its enzymatic activity reduced sixfold in retinoic acid-treated keratinocytes (p < 0.01, n = 4).These results demonstrate that retinoic acid treatment in vivo, in contrast to in vitro, leads to not only increased transglutaminase-K protein expression but also increased enzymatic activity in the absence of detectable increases in mRNA levels.These data, taken with the previously reported lack of in vivo modulation of the differentiation markers keratins 1 and 10 by retinoic acid, indicate that certain aspects of keratinocyte terminal differentiation that are altered in vitro by retinoic acid do not occur in vivo in human skin