Retinoblastoma protein 1 (RB1) is encoded by a tumor suppressor gene that was discovered more than 30 years ago. Almost all mitogenic signals promote cell cycle progression by braking on the function of RB1 protein through mono- and subsequent hyper-phosphorylation mediated by cyclin-CDK complexes. The loss of RB1 function drives tumorigenesis in limited types of malignancies including retinoblastoma and small cell lung cancer. In a majority of human cancers, RB1 function is suppressed during tumor progression through various mechanisms. The latter gives rise to the acquisition of various phenotypes that confer malignant progression. The RB1-targeted molecules involved in such phenotypic changes are good quarries for cancer therapy. Indeed, a variety of novel therapies have been proposed to target RB1 loss. In particular, the inhibition of a number of mitotic kinases appeared to be synthetic lethal with RB1 deficiency. A recent study focusing on a neighboring gene that is often collaterally deleted together with RB1 revealed a pharmacologically targetable vulnerability in RB1-deficient cancers. Here we summarize current understanding on possible therapeutic approaches targeting functional or genomic aberration of RB1 in cancers.

Dietary fat consumption during accelerated stages of mammary gland development such as peripubertal maturation or pregnancy is known to increase the risk for breast cancer. However, the underlying molecular mechanisms are not fully understood. Here we examined the gene expression profile of mouse mammary epithelial cells (MMECs) on exposure to a high‐fat diet (HFD) or control diet (CD). Trp53 ^‐/‐ female mice were fed with the experimental diets for 5 weeks during the peripubertal period (3 to 8 weeks of age). The treatment showed no significant difference in the body weight between the HFD‐fed mice and CD‐fed mice. However, gene set enrichment analysis (GSEA) predicted a significant enrichment of c‐Myc target genes in animals fed HFD. Furthermore, we detected enhanced activity and stabilization of c‐Myc protein in MMECs exposed to a HFD. This was accompanied by augmented c‐Myc phosphorylation at S62 with a concomitant increase in extracellular receptor kinase (ERK) phosphorylation. Moreover, MMECs derived from HFD‐fed Trp53 ^‐/‐ mouse showed increased colony and sphere forming potential that was dependent on c‐Myc. We further found that oleic acid, a major fatty acid constituent of the HFD, and TAK‐875, an agonist to G protein‐coupled receptor 40 (GPR40, a receptor for oleic acid), were shown to enhance c‐Myc stabilization and MMEC proliferation. Overall, our data indicate that HFD influences MMECs by stabilizing an oncoprotein, pointing to a novel mechanism underlying the dietary fat‐mediated mammary carcinogenesis.