Genotoxic stress triggers signalling pathways that mediate either the protection or killing of affected cells. Whereas induction of p53 involves events in the cell nucleus, the activation of transcription factors AP-1 and NF-kappaB by ultraviolet radiation is mediated through membrane-associated signalling proteins, ruling out a nuclear signal. An early event in AP-1 induction by ultraviolet radiation is activation of Jun kinases (JNKs), which mediate the induction of the immediate-early genes c-jun and c-fos. The JNKs have also been proposed to mediate the apoptopic response to genotoxins. The non-receptor tyrosine kinase c-Abl is also activated by genotoxic stress. To understand the relationship between these events, we compared the activation of p53, JNK and c-Abl by several DNA-damaging agents in murine fibroblasts. We found that whereas p53 was induced by every genotoxic stimulus tested, c-Abl was activated by most stimuli except ultraviolet irradiation and JNK was strongly stimulated only by ultraviolet light and the alkylating agent methyl methanesulphonate. Activation of JNK by this alkylating agent was normal in c-Abl-null cells but was reduced in c-Src-null cells. Unlike p53 induction, c-Abl activation occurs in the S phase of the cell cycle and does not affect cell proliferation. These findings show that signals generated by genotoxins are transduced by multiple, independent pathways. Only p53 appears to be a universal sensor of genotoxic stress.

The activation of the mitogenic program by v-Abl tyrosine kinase requires not only Ras but also Rac. Multiple pathways are activated by v-Abl in transformed cells. The availability of some of these pathways may determine whether v-Abl can activate mitogenesis.

Vulvar intraepithelial neoplasias (VINs) are potentially premalignant lesions of the squamous mucosa. The immunohistochemical distribution of the catalytic protein subunit of telomerase (hTERT) and the patterns of X chromosome inactivation were investigated as markers of neoplasia in samples from a patient with multifocal and diffuse VIN. hTERT nuclear staining in VIN correlated with squamous maturation and the degree of nuclear atypia. Normal mucosa revealed faint nuclear staining of parabasal cells and lower intermediate layer squamous cells. Monoclonal composition was demonstrated in 0 of 3 samples of VIN1, 2 of 3 samples of VIN2, and 13 of 13 samples of VIN3. The patterns of X chromosome inactivation indicated intramucosal extension and multifocal origin of individual lesions. Five samples of histologically normal vulvar squamous epithelium revealed a random pattern of X chromosome inactivation, consistent with polyclonal composition. All 19 samples from 9 lesions contained human papillomavirus (HPV)-16 sequences. Neither mutations in the p53 tumor suppressor gene or K-ras oncogenes nor loss of heterozygosity at 7 chromosomal loci were detected in any of the 19 samples of VIN. These results demonstrate that HPV-associated VIN may result from multifocal and diffuse 2-dimensional intraepithelial expansion of an immortalized monoclonal cell population.