Complex diseases such as cancer are often associated with aberrant gene expression at both the transcriptional and post-transcriptional level. In the past several years, competing endogenous RNAs (ceRNAs) have emerged as an important class of post-transcriptional regulators that alter gene expression through a microRNA-mediated mechanism. Recent studies in both solid tumors and hematopoietic malignancies showed that ceRNAs play significant roles in cancer pathogenesis by altering the expression of key tumorigenic or tumor suppressive genes. Characterizing the identity, function and mechanism of the ceRNAs will not only further our fundamental understanding of RNA-mediated cancer pathogenesis, but also may shed light on developing new RNA-based therapeutic strategies for treating cancer.

Overwhelming evidence indicates that virtually all treatment-naive tumors contain a subpopulation of cancer cells that possess some stem cell traits and properties and are operationally defined as cancer cell stem cells (CSCs). CSCs manifest inherent heterogeneity in that they may exist in an epithelial and proliferative state or a mesenchymal non-proliferative and invasive state. Spontaneous tumor progression, therapeutic treatments, and (epi)genetic mutations may also induce plasticity in non-CSCs and reprogram them into stem-like cancer cells. Intrinsic cancer cell heterogeneity and induced cancer cell plasticity, constantly and dynamically, generate a pool of CSC subpopulations with varying levels of epigenomic stability and stemness. Despite the dynamic and transient nature of CSCs, they play fundamental roles in mediating therapy resistance and tumor relapse. It is now clear that the stemness of CSCs is coordinately regulated by genetic factors and epigenetic mechanisms. Here, in this perspective, we first provide a brief updated overview of CSCs. We then focus on microRNA-34a (miR-34a), a tumor-suppressive microRNA (miRNA) devoid in many CSCs and advanced tumors. Being a member of the miR-34 family, miR-34a was identified as a p53 target in 2007. It is a bona fide tumor suppressor, and its expression is dysregulated and downregulated in various human cancers. By targeting stemness factors such as NOTCH, MYC, BCL-2, and CD44, miR-34a epigenetically and negatively regulates the functional properties of CSCs. We shall briefly discuss potential reasons behind the failure of the first-in-class clinical trial of MRX34, a liposomal miR-34a mimic. Finally, we offer several clinical settings where miR-34a can potentially be deployed to therapeutically target CSCs and advanced, therapy-resistant, and p53-mutant tumors in order to overcome therapy resistance and curb tumor relapse.

Matrix metalloproteinases (MMP) contribute to tumor microenvironment and are associated with bladder cancer. A study examining the association between MMP polymorphisms and bladder cancer risk has never been published. We analyzed the association of 11 single nucleotide polymorphisms (SNPs) and one microsatellite polymorphism in MMP genes MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, and MMP-12 with bladder cancer risk in 560 Caucasian patients and 560 controls matched on age, gender, and ethnicity. Individual, combination, haplotype, and diplotype analyses were done. No associations between individual MMP polymorphisms and overall bladder cancer risk were seen. The MMP-9 microsatellite z24 CA repeat allele and the MMP-12-82 GG polymorphisms were associated with invasive bladder cancer risk [odds ratio (OR), 2.60; 95% confidence interval (95% CI), 1.07-6.26; and OR, 4.59; 95% CI, 1.21-17.32, respectively]. Smoke-stratified analyses revealed several associations between MMP polymorphisms, alone and in combination, with bladder cancer risk, particularly in light smokers. Linkage disequilibrium was seen in all of the MMP-1, MMP-3, MMP-8, and MMP-12 SNPs and in four of five MMP-9 polymorphisms tested. Several MMP-9 haplotype and diplotypes were associated with overall and invasive bladder cancer risk. Our study suggests that genetic variations in the MMP family are associated with bladder cancer risk. Heavy carcinogen exposure may overwhelm some of the genetic effects of MMP polymorphisms. Our study confirms the importance of taking a multigenic pathway-based approach to risk assessment. (Cancer Res 2006; 66(24): 11644-8)

Purpose: Matrix metalloproteinases (MMP) promote tumor invasion and alter microenvironment. MMP levels are elevated in bladder cancer patients correlating with more advanced stage. We tested whether polymorphisms in MMP genes modify the risk of bladder cancer invasiveness and whether smoke exposure modifies this risk. Experimental Design: Using a case-only study, we examined the association of 11 singlenucleotide polymorphisms and one microsatellite polymorphism in MMP genes MMP1, MMP2, MMP3, MMP8, MMP9, and MMP12 with the risk of invasive bladder cancer in 243 Caucasian patients with muscle invasive compared with 315 Caucasian patients with superficial disease. Results: The MMP9 microsatellite z24 CA repeat and MMP12 -82 G alleles were associated with a higher risk of bladder cancer invasiveness [odds ratio (OR), 3.10; 95% confidence interval (95% CI) 1.17-8.23 and OR, 1.50; 95% CI, 1.00-2.28, respectively]. Ever smokers with the MMP9 z24 CA repeat allele had a 5.16-fold (95% CI, 1.56-17.1) increased risk of invasiveness compared with wild-type never smokers. Ever smokers with the MMP12 G allele also had an increased risk of bladder cancer invasiveness (OR, 2.32; 95% CI, 1.30-4.12). Conclusions: Our results suggest that genetic changes in MMPs are associated with the development of invasive bladder cancer.