Characterization of cell clones stably transfected with short form caspase-9: apoptotic resistance and Bcl-XL expression

Heat shock factor 1 induces crystallin-αB to protect against cisplatin nephrotoxicity

Cisplatin, a wildly used chemotherapy drug, induces nephrotoxicity that is characterized by renal tubular cell apoptosis. In response to toxicity, tubular cells can activate cytoprotective mechanisms, such as the heat shock response. However, the role and regulation of the heat shock response in cisplatin-induced nephrotoxicity remain largely unclear. In the present study, we demonstrated the induction of heat shock factor (Hsf)1 and the small heat shock protein crystallin-αB (CryAB) during cisplatin nephrotoxicity in mice. Consistently, cisplatin induced Hsf1 and CryAB in a cultured renal proximal tubular cells (RPTCs). RPTCs underwent apoptosis during cisplatin treatment, which was increased when Hsf1 was knocked down. Transfection or restoration of Hsf1 into Hsf1 knockdown cells suppressed cisplatin-induced apoptosis, further supporting a cytoprotective role of Hsf1 and its associated heat shock response. Moreover, Hsf1 knockdown increased Bax translocation to mitochondria and cytochrome c release into the cytosol. In RPTCs, Hsf1 knockdown led to a specific downregulation of CryAB. Transfection of CryAB into Hsf1 knockdown cells diminished their sensitivity to cisplatin-induced apoptosis, suggesting that CryAB may be a key mediator of the cytoprotective effect of Hsf1. Taken together, these results demonstrate a heat shock response in cisplatin nephrotoxicity that is mediated by Hsf1 and CryAB to protect tubular cells against apoptosis.

Overexpression of BLCAP induces S phase arrest and apoptosis independent of p53 and NF-κB in human tongue carcinoma

Bladder cancer-associated protein gene (BLCAP) is a novel candidate tumor suppressor gene identified from the human bladder carcinoma. Our previous studies have shown that BLCAP overexpression could inhibit cell growth by inducing apoptosis in HeLa cells [Zuo Z, Zhao M, Liu J, Gao G, Wu X: Tumor Biol 27: 221-226, 2006]. Such evidence suggests the alterations in BLCAP may play an important role in tumorigenesis. To further study the biological function of the BLCAP gene, we constructed a recombinant retroviral vector encoding BLCAP cDNA. Overexpressed BLCAP, via stable infection of exogenous BLCAP, resulted in growth inhibition of the human tongue cancer cell line Tca8113 in vitro, accompanied by S phase cell cycle arrest and apoptosis. The growth inhibition was correlated with up-regulation of p21(WAF1/CIP1 )expression and down-regulation of Bcl-XL and Bcl-2 expressions. However, p53 expression and NF-kappaB activity remained unchanged post infection. Furthermore, no changes in p53 phosphorylation at Ser46 and nuclear localization, which are critical to p53 function, were observed in BLCAP-overexpressed cells. Taken together, BLCAP may play a role not only in regulating cell proliferation but also in coordinating apoptosis and cell cycle via a novel way independent of p53 and NF-kappaB.

Characterization of cell clones isolated from hypoxia-selected renal proximal tubular cells

Under hypoxia, some cells survive and others are irreversibly injured and die. The factors that determine cell fate under stress remain largely unknown. We recently selected death-resistant cells via repeated episodes of hypoxia. In the present study, 80 clones were isolated from the selected cells and their response to apoptotic injury was characterized. Compared with the wild-type cells, the isolated clones showed a general resistance to apoptosis: 13 were extremely resistant to azide-induced apoptosis, 10 to staurosporine, and 9 to cisplatin. The cell clones that most consistently demonstrated resistance or sensitivity to injury were further studied for their response to azide treatment. Azide induced comparable ATP depletion in these clones and wild-type cells. Hypoxia inducible factor-1 (HIF-1) was upregulated in several clones, but the upregulation did not correlate with cell death resistance. The selected clones maintained an epithelial phenotype, showing typical epithelial morphology, forming "domes" at high density, and expressing E-cadherin. Azide-induced Bax translocation and cytochrome c release, two critical mitochondrial events of apoptosis, were abrogated in death-resistant clones. In addition, cell lysates isolated from these clones showed lower caspase activation on addition of exogenous cytochrome c. Bax, Bak, and Bid expression in these clones was similar to that in wild-type cells, whereas Bcl-2 expression was higher in all the selected clones and, interestingly, Bcl-xL was markedly upregulated in the most death-resistant clones. The results suggest that apoptotic resistance of the selected clones is not determined by a single factor or molecule but, rather, by various alterations at the core apoptotic pathway.

Yeast elf1 factor is phosphorylated and interacts with protein kinase CK2

One of the biggest group of proteins influenced by protein kinase CK2 is formed by factors engaged in gene expression. Here we have reported recently identified yeast transcription elongation factor Elf1 as a new substrate for both monomeric and tetrameric forms of CK2. Elf1 serves as a substrate for both the recombinant CK2alpha' (K(m) 0.38 microM) and holoenzyme (K(m) 0.13 microM). By MALDI-MS we identified the two serine residues at positions 95 and 117 as the most probable in vitro phosphorylation sites. Coimmunoprecypitation experiments show that Elf1 interacts with catalytic (alpha and alpha') as well as regulatory (beta and beta') subunits of CK2. These data may help to elucidate the role of protein kinase CK2 and Elf1 in the regulation of transcription elongation.