Rats subjected to chronic inhalation exposure of formaldehyde develop nasal squamous cell carcinomas. Decreased activity of which of the following genes is likely to be found on cytogenetic studies of the tumor cells?

Question

Rats subjected to chronic inhalation exposure of formaldehyde develop nasal squamous cell carcinomas.  Decreased activity of which of the following genes is likely to be found on cytogenetic studies of the tumor cells?

Quizplus · Accepted Answer

Decreased activity of a tumor suppressor gene would predispose to neoplasms. Of the choices listed, p53 is the only tumor suppressor gene. In normal individuals, p53 regulates cell proliferation. It acts during phase G1 of the cell cycle to detect abnormalities of the cellular genome. If there is damaged DNA, p53 will prevent the cell from progressing to mitosis, causing the cell to be arrested in the G1 phase. If the DNA can be repaired, the cell will subsequently be allowed to divide, but if the damage is so severe that repair is impossible, the cell will proceed instead to apoptosis. p53 is nicknamed "the molecular policeman" because of its important role in guarding the integrity of genetic material. (Choice A) The bcr-abl fusion gene is a product of translocation of genetic material from chromosome 9 to chromosome 22 [t(9;22)]. It codes for a protein with tyrosine kinase activity. The bcr-abl translocation is the Philadelphia chromosome found in chronic myelogenous leukemia. (Choice B) The ras proto-oncogene codes a protein that participates in signal transduction (MAP-kinase associated pathway). Over-expression of this gene leads to increased sensitivity of cells to mitogenic stimuli. This mutation occurs in a large number of cancers. (Choice C) The Erb-B2 gene encodes a protein with tyrosine kinase activity related to the epidermal growth factor receptor. Over-expression of this proto-oncogene is associated with breast and ovarian cancers. (Choice E) Expression of the N-myc proto-oncogene is amplified in neuroblastoma. Educational Objective: p53 is a tumor suppressor gene that controls cell division and apoptosis. It is inactivated in many tumors.

Rats Subjected to Chronic Inhalation Exposure of Formaldehyde Develop Nasal