1. Field of the Invention
The present invention relates generally to the fields of molecular biology, genetics and oncology. More particularly, it concerns semaphorin 3B and its use in cancer therapy and diagnosis.
2. Description of Related Art
The semaphorin family is comprised of secreted and membrane associated proteins that contribute to axonal path finding during neural development by repulsing axons, inhibiting growth cone extension and causing collapse of growth cones (Nakamura et al., 2000; Raper, 2000; Tamagnone and Comoglio, 2000). The SEMA3 family members encode secreted proteins that signal through binding to neuropilin receptors (NP) interacting with plexins (Nakamura et al., 2000; Raper, 2000; Tamagnone and Comoglio, 2000). Several semaphorins are expressed in adult non-neuronal tissues suggesting other functions. For example, SEMA3A inhibited the motility of aortic endothelial cells expressing NP1, disrupted the formation of lamellipodia, induced depolymerization of F-actin (Miao et al., 1999), and inhibited branching morphogenesis in the fetal mouse lung (Ito et al., 2000). However, the roles of SEMA3B and SEMA3F in non-neuronal cells and human cancer are unknown.
Loss of heterozygosity of chromosome 3p sequences is a critical event in the pathogenesis of lung and other cancers and directed a tumor suppressor gene (TSG) search to this region. Multiple distinct 3p regions are involved in human lung cancer pathogenesis including one at 3p21.3, where the inventors identified 19 candidate TSGs were identified. This defined 3p21.3 region undergoes allele loss in ˜80% of primary lung cancers and ˜40% of preneoplastic or normal epithelial samples of smoking damaged lung, marking it as one of the first sites involved (Wistuba et al., 2000). Two of the 19 genes are semaphorin family members (SEMA3B and SEMA3F) lying ˜70 kb apart (Sekido et al., 1996). In assessing the TSG candidacy of SEMA3B and SEMA3F, only a few mutations were found, but loss of expression of SEMA3B mRNA was common, occurring in ˜80% of lung cancers.
On the other hand, the inventors and others have found no SEMA3F mutations, and loss of SEMA3F expression in 18%, of these same lung cancers (Sekido et al., 1996; Xiang et al., 1996). However, recent immunohistochemical studies of lung cancers, found reduction of SEMA3F expression in higher stages of lung cancer, and a change in SEMA3F localization from the membrane to the cytoplasm compared to normal lung epithelium (Brambilla et al., 2000). In addition, functional studies using a P1 clone containing SEMA3F (and potentially SEMA3B) showed tumor suppressive effect for mouse A9 fibrosarcoma cells (Todd et al., 1996). Recent studies have implicated tumor acquired promoter hypermethylation as a mechanism of inactivation of mRNA expression of TSGs in the pathogenesis of several human cancers (Baylin et al., 1998). In fact, the inventors and others have found that one isoform at the RASSF1 locus, RASSF1A, located ˜60 kb centromeric of SEMA3B, underwent tumor acquired promoter methylation, leading to inactivated expression in lung and breast tumors (Dammann et al., 2000; Burbee et al., 2001).
Thus, although the 3p region has been implicated in cancer development and progression, it is not completely clear which genes in this region are involved. Thus, further information on these issues is needed.