MicroRNAs play important roles in animal development, cell differentiation, and metabolism and have been implicated in human cancer. The let-7 microRNA controls the timing of cell cycle exit and terminal differentiation in Caenorhabditis elegans and is poorly expressed or deleted in human lung tumors. Here, we show that let-7 is highly expressed in normal lung tissue, and that inhibiting let-7 function leads to increased cell division in A549 lung cancer cells. Overexpression of let-7 in cancer cell lines alters cell cycle progression and reduces cell division, providing evidence that let-7 functions as a tumor suppressor in lung cells. let-7 was previously shown to regulate the expression of the RAS lung cancer oncogenes, and our work now shows that multiple genes involved in cell cycle and cell division functions are also directly or indirectly repressed by let-7. This work reveals the let-7 microRNA to be a master regulator of cell proliferation pathways. [Cancer Res 2007;67(16):7713-22]

Lung cancer is the leading cause of cancer deaths worldwide, yet few genetic markers of lung cancer risk useful for screening exist. The let-7 family-of-microRNAs (miRNA) are global genetic regulators important in controlling lung cancer oncogene expression by binding to the 3 ¶ untranslated regions of their target mRNAs. The purpose of this study was to identify single nucleotide polymorphisms (SNP) that could modify let-7 binding and to assess the effect of such SNPs on target gene regulation and risk for non-small cell lung cancer (NSCLC). let-7 complementary sites (LCS) were sequenced in the KRAS 3 ¶ untranslated region from 74 NSCLC cases to identify mutations and SNPs that correlated with NSCLC. The allele frequency of a previously unidentified SNP at LCS6 was characterized in 2,433 people (representing 46 human populations). The frequency of the variant allele is 18.1% to 20.3% in NSCLC patients and 5.8% in world populations. The association between the SNP and the risk for NSCLC was defined in two independent case-control studies. A case-control study of lung cancer from New Mexico showed a 2.3-fold increased risk (confidence interval, 1.1-4.6; P = 0.02) for NSCLC cancer in patients who smoked <40 pack-years. This association was validated in a second independent case-control study. Functionally, the variant allele results in KRAS overexpression in vitro. The LCS6 variant allele in a KRAS miRANA complementary site is significantly associated with increased risk for NSCLC among moderate smokers and represents a new paradigm for let-7 miRNAs in lung cancer susceptibility. [Cancer Res 2008;68(20):8535-40]

Ovarian cancer (OC) is the single most deadly form of women's cancer, typically presenting as an advanced disease at diagnosis in part due to a lack of known risk factors or genetic markers of risk. The KRAS oncogene and altered levels of the microRNA (miRNA) let-7 are associated with an increased risk of developing solid tumors. In this study, we investigated a hypothesized association between an increased risk of OC and a variant allele of KRAS at rs61764370, referred to as the KRAS-variant, which disrupts a let-7 miRNA binding site in this oncogene. Specimens obtained were tested for the presence of the KRAS-variant from nonselected OC patients in three independent cohorts, two independent ovarian case-control studies, and OC patients with hereditary breast and ovarian cancer syndrome (HBOC) as well as their family members. Our results indicate that the KRAS-variant is associated with more than 25% of nonselected OC cases. Further, we found that it is a marker for a significant increased risk of developing OC, as confirmed by two independent case-control analyses. Lastly, we determined that the KRAS-variant was present in 61% of HBOC patients without BRCA1 or BRCA2 mutations, previously considered uninformative, as well as in their family members with cancer. Our findings strongly support the hypothesis that the KRAS-variant is a genetic marker for increased risk of developing OC, and they suggest that the KRAS-variant may be a new genetic marker of cancer risk for HBOC families without other known genetic abnormalities. Cancer Res; 70(16); 6509-15. ©2010 AACR.

Bone morphogenetic protein (BMP) pathways control an array of developmental and homeostatic events, and must themselves be exquisitely controlled. Here, we identify Caenorhabditis elegans SMA-10 as a positive extracellular regulator of BMP–like receptor signaling. SMA-10 acts genetically in a BMP–like (Sma/Mab) pathway between the ligand DBL-1 and its receptors SMA-6 and DAF-4. We cloned sma-10 and show that it has fifteen leucine-rich repeats and three immunoglobulin-like domains, hallmarks of an LRIG subfamily of transmembrane proteins. SMA-10 is required in the hypodermis, where the core Sma/Mab signaling components function. We demonstrate functional conservation of LRIGs by rescuing sma-10(lf) animals with the Drosophila ortholog lambik, showing that SMA-10 physically binds the DBL-1 receptors SMA-6 and DAF-4 and enhances signaling in vitro. This interaction is evolutionarily conserved, evidenced by LRIG1 binding to vertebrate receptors. We propose a new role for LRIG family members: the positive regulation of BMP signaling by binding both Type I and Type II receptors.

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While cancer is a serious health issue, there are very few genetic biomarkers that predict predisposition, prognosis, diagnosis, and treatment response. Recently, sequence variations that disrupt microRNA (miRNA)-mediated regulation of genes have been shown to be associated with many human diseases, including cancer. In an early example, a variant at one particular single nucleotide polymorphism (SNP) in a let-7 miRNA complementary site in the 3' untranslated region (3' UTR) of the KRAS gene was associated with risk and outcome of various cancers. The KRAS oncogene is an important regulator of cellular proliferation, and is frequently mutated in cancers. To discover additional sequence variants in the 3' UTR of KRAS with the potential as genetic biomarkers, we resequenced the complete region of the 3' UTR of KRAS in multiple non-small cell lung cancer and epithelial ovarian cancer cases either by Sanger sequencing or capture enrichment followed by high-throughput sequencing. Here we report a comprehensive list of sequence variations identified in cases, with some potentially dysregulating expression of KRAS by altering putative miRNA complementary sites. Notably, rs712, rs9266, and one novel variant may have a functional role in regulation of KRAS by disrupting complementary sites of various miRNAs, including let-7 and miR-181.

Background: In C. elegans there are two well-defined TGFβ-like signaling pathways. The Sma/Mab pathway affects body size morphogenesis, male tail development and spicule formation while the Daf pathway regulates entry into and exit out of the dauer state. To identify additional factors that modulate TGFβ signaling in the Sma/Mab pathway, we have undertaken a genetic screen for small animals and have identified kin-29.Results: kin-29 encodes a protein with a cytoplasmic serine-threonine kinase and a novel Cterminal domain. The kinase domain is a distantly related member of the EMK (ELKL motif kinase) family, which interacts with microtubules. We show that the serine-threonine kinase domain has in vitro activity. kin-29 mutations result in small animals, but do not affect male tail morphology as do several of the Sma/Mab signal transducers. Adult worms are smaller than the wild-type, but also develop more slowly. Rescue by kin-29 is achieved by expression in neurons or in the hypodermis. Interaction with the dauer pathway is observed in double mutant combinations, which have been seen with Sma/Mab pathway mutants. We show that kin-29 is epistatic to the ligand dbl-1, and lies upstream of the Sma/Mab pathway target gene, lon-1. Conclusion:kin-29 is a new modulator of the Sma/Mab pathway. It functions in neurons and in the hypodermis to regulate body size, but does not affect all TGFβ outputs, such as tail morphogenesis.

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