About a third of all human cancers harbor mutations in one of the K-, N-, or HRAS genes that encode an abnormal RAS protein locked in a constitutively activated state to drive malignant transformation and tumor growth.
It can be concluded that the organophosphorous pesticides parathion and malathion induced malignant transformation of breast cells through genomic instability altering p53 and c-Ha-ras, considered pivotal to cancer process.
At present, K-ras-2 mutation is not useful for differentiating pancreatic cancer from chronic pancreatitis or the identification of patients with chronic pancreatitis at risk for malignant transformation.
To better understand the molecular changes responsible for this increased risk of malignant transformation, we examined the expression of c-fos and c-Ha-ras, proto-oncogenes known to be involved in cellular proliferation and transformation, in chronic wounds.
These results showed that the unmutated human c-H-ras gene facilitates malignant transformation of hepatocytes when continuous liver-cell death and regeneration is caused by repeated administration of CCl4.
The different p21ras expression among the type of tumors may represent the state of tumor cells differentiation with greater expression with more immaturity in the melanocyte lineage. p21ras expression does not appear to represent a marker of malignant transformation.
Transfection of pHO6T1 into two other infinite life-span human fibroblast cell lines, cells that had not been transfected with v-myc, also resulted in malignant transformation, suggesting that the infinite life-span phenotype of MSU-1.1 cells, and not necessarily expression of the v-myc oncogene, was the factor that complemented T24 HRAS expression to cause malignant transformation.
The expression of v-Ha-ras is associated with a loss of the high (but not low) affinity binding component of the EGF-R. Malignant transformation and loss of TGF alpha/EGF responsiveness did not correlate with an increase in TGF alpha production.
This immunohistochemical study examined the relationship between p21ras expression and malignant transformation, cellular differentiation, and proliferative activity in vivo. p21ras was found to be widely expressed in normal tissues, but within those tissues expression was often sharply restricted to cells at specific stages of differentiation; terminally differentiated cells generally showed stronger reactivity with antibodies to p21ras than did rapidly proliferating cells.
Finally, we demonstrate that, like the N- and c-myc genes, the L-myc gene can cooperate with a mutant Ha-ras gene to cause malignant transformation of rat embryo fibroblasts in culture.
Southern blot analysis of BamHl-digested genomic DNA from the Ecogpt-transformed clones indicated that rapid malignant transformation was associated with integration of a complete copy of the 6.6-kilobase fragment of pEJ containing the activated c-Ha-ras gene.