Cellular and molecular biological aspects of human bronchogenic carcinogenesis

Abstract

This is a time of rapid progress in the field of human bronchogenic carcinogenesis due to recent advances in cellular and molecular biology. Important developments over the last 10 years include establishment of methods for culturing NHBE cells under defined conditions, and molecular biological and biochemical epidemiological techniques for identifying genetic changes that are associated with malignant transformation of these cells. Most progress in defining genes associated with human carcinogenesis has been due to discoveries related to oncogenes and more recently, tumor suppressor genes. As was described in Section II.B.3.a, we now know that oncogene products serve as growth factors, growth factor receptors, and cytosolic and nuclear regulatory proteins. In addition, although the actions of putative tumor suppressor genes are less well understood, the first isolated tumor suppressor gene Rb, interacts with the products of DNA viruses which, in turn, are involved in regulation of transcription as was described in Section II.B.3.b. Thus, not surprisingly, both oncogenes and tumor suppressor genes code for classes of proteins that are known to play an important role in regulation of cell proliferation. Recently, a second gene that appears to possess tumor suppression activity (p53) has been identified on the short arm of chromosome 17 (17p). The initial data suggesting a possible tumor suppressor gene on chromosome 17p came from cytogenetic and RFLP studies associating loss of heterozygosity in the chromosome 17p13 region with tumor cells and tissues. Since the p53 gene is located in this region it was evaluated and found to be frequently or always altered in several types of tumor cells. Recently, it was determined that introduction of the wild-type p53 gene into NIH3T3 cells will inhibit subsequent malignant transformation. Thus, the preponderance of evidence now supports the hypothesis that while mutated p53 acts as an oncogene, the wild-type p53 gene codes for a tumor suppressor function. The role of balance between oncogenes and tumor suppressor genes in control of proliferation is presently an active area of investigation. As discussed, introduction of a chromosome containing a tumor suppressor gene will suppress tumorigenicity of a malignant cell line, even though that cell line possesses an active c-Ha-ras oncogene. Whether or not the level of expression of an activated oncogene is related to tumorigenicity is presently being investigated.(ABSTRACT TRUNCATED AT 400 WORDS)