👤 Carolina N Perez

The common fragile sites are regions of profound genomic instability found in all individuals. The full size of each region of instability ranges from under one megabase (Mb) to greater than 10 Mbs. At least half of the CFS regions have been found to span extremely large genes that spanned from 600 kb to greater than 2.0 Mbs. The large CFS genes are also very interesting from a cancer perspective as several of them, including FHIT and WWOX, have already demonstrated the capacity to function as tumor suppressor genes, both in vitro and in vivo. We estimate that there may be 40-50 large genes localized in CFS regions. The expression of a number of the large CFS genes has been previously shown to be lost in many different cancers and this is frequently associated with a worse clinical outcome for patients. To determine if there was selection for the inactivation of different large CFS genes in different cancers, we examined the expression of 13 of the 20 known large CFS genes: FHIT, WWOX, PARK2, GRID2, NBEA, DLG2, RORA isoforms 1 and 4, DAB1, CNTNAP2, DMD, IL1RAPL1, IMMP2L and LARGE in breast, ovarian, endometrial and brain cancers using real-time RT-PCR analysis. Each cancer had a distinct profile of different large CFS genes that were inactivated. Interestingly, in breast, ovarian and endometrial cancers there were some cancers that had inactivation of expression of none or only one of the tested genes, while in other specimens there was inactivation of multiple tested genes. Brain cancers had inactivation of many of the tested genes, a number of which function in normal neurological development. We find that there is no relationship between the frequency that any specific CFS is expressed and the frequency that the gene from that region is inactivated in different cancers. Instead, it appears that different cancers select for the inactivation of different large CFS genes. Show less

Schizosaccharomyces pombe rho1(+) is required for maintenance of cell integrity and polarization of the actin cytoskeleton. However, no other effector besides the (1,3)beta-D-glucan synthase enzyme has been identified in S. pombe. We have further investigated if rho1(+ )signalling could be also mediated by the two protein kinase C homologues, pck1p and pck2p. We show in this study that both kinases interact with rho1p and rho2p only when bound to GTP, as most GTPase effectors do. Interestingly, the interaction was mapped in a different part of the proteins than in Saccharomyces cerevisiae Pkc1p. Thus, active rho1p binds to the amino-terminal region of the pcks where two HR1 motifs are located, and binding to the GTPase dramatically stabilizes the kinases. Detailed biochemical analysis suggests that pck2p is more important in the regulation of the enzyme (1-3)beta-D-glucan synthase. Thus, overexpression of pck2(+), but not pck1(+), caused a general increase in cell wall biosynthesis, mainly in beta-glucan, and (1-3)beta-D-glucan synthase activity was considerably augmented. When this activity was separated into soluble and membrane fractions and reconstituted, the increase caused by pck2(+) overexpression was exclusively detected in the membrane component. We also show that both protein kinase C homologues are required for the maintenance of cell integrity. pck1delta and pck2delta strains present a number of defects related to the cell wall, indicating that this structure might be co-ordinately regulated by both kinases. In addition, pck2p, but not pck1p, seems to be involved in keeping cell polarity. Genetic evidence indicates that both pck1(+) and pck2(+) interact with cps1(+) and gls2(+), two genes similar to S. cerevisiae FKS1 and FKS2 that encode membrane subunits of the (1-3)beta-D-glucan synthase. pck1(+ )also showed a genetic interaction with ras1(+) and ral1(+) suggesting the existence of a functional link between both signalling pathways. Show less