RasGTPase-activating protein is a target of caspases in spontaneous apoptosis of lung carcinoma cells and in response to etoposide

p120 RasGTPase-activating protein (RasGAP), the main regulator of Ras GTPase family members, is cleaved at low caspase activity into an N-terminal fragment that triggers potent anti-apoptotic signals via activation of the Ras/PI-3 kinase/Akt pathway. When caspase activity is increased, RasGAP fragment N is further processed into two fragments that effectively potentiate apoptosis. Expression of RasGAP protein and its cleavage was assessed in human lung cancer cells with different histology and responsiveness to anticancer drug-induced apoptosis. Here we show that therapy-sensitive small lung carcinoma cell (SCLC) lines have lower RasGAP expression levels and higher spontaneous cleavage with formation of fragment N compared to therapy-resistant non-small cell lung carcinoma cell (NSCLC) lines. The first RasGAP cleavage event strongly correlated with the increased level of spontaneous apoptosis in SCLC. However, generation of protective RasGAP fragment N also related to the potency of SCLC to develop secondary therapy-resistance. In response to etoposide (ET), RasGAP fragment N was further cleaved in direct dependence on caspase-3 activity, which was more pronounced in NSCLC cells. Caspase inhibition, while effectively preventing the second cleavage of RasGAP, barely affected the first cleavage of RasGAP into fragment N that was always detectable in NSCLC and SCLC cells. These findings suggest that different levels of RasGAP and fragment N might play a significant role in the biology and different clinical course of both subtypes of lung neoplasms. Furthermore, constitutive formation of RasGAP fragment N can potentially contribute to primary resistance of NSCLC to anticancer therapy by ET but also to secondary therapy-resistance in SCLC

Expression of DNA damage response proteins and complete remission after radiotherapy of stage IB–IIA of cervical cancer

The primary aim of this study was to investigate if the expression of the DNA damage identifying protein DNA-PKcs known to be involved in DNA repair after treatment with ionising radiation can be used as a predictive marker for radiotherapy (RT) response in cervical cancer. Formalin-fixed primary tumour biopsies from 109 patients with cervical cancer, FIGO-stage IB–IIA, treated with preoperative brachytherapy followed by radical surgery were analysed by immunohistochemistry. In addition, correlation studies between early pathological tumour response to radiation and expression of Ku86, Ku70, Mdm-2, p53 and p21 in primary tumours were also performed. We found that tumour-transformed tissue shows positive immunostaining of DNA-PKcs, Ku86 and Ku70, while non-neoplastic squamous epithelium and tumour-free cervix glands show negative immunoreactivity. Expression of DNA-PKcs positively correlated with both Ku86 and Ku70, and a statistically significant correlation between the Ku subunits was also found. After RT, 85 patients demonstrated pathologic complete remission (pCR), whereas 24 patients had residual tumour in the surgical specimen (non-pCR). The main finding of our study is that there was no correlation between the outcome of RT and the expression of DNA-PK subunits. Positive p53 tumours were significantly more common among non-pCR cases than in patients with pCR (P=0.031). Expression of p21 and Mdm-2 did not correlate with the outcome of RT