The secreted class 3 semaphorins, which include SEMA3F, a tumor-suppressor gene in lung cancer, were initially identified as molecules involved in the repulsion of developing nerve growth cones. These molecules are part of a larger family that includes transmembrane and membrane-associated proteins, some of which are expressed widely and implicated in other functions such as development and immune response.1 SEMA3B and SEMA3F are both encoded in 3p21.3,2–4 a region of frequent loss of heterozygosity in lung cancer,5 which initially suggested that one or both of these genes might have tumor-suppressor activity.
