Sahar Baig

Introduction. Colorectal cancer (CRC) is one of the most common causes of cancer mortality in the US, accounting for around 850,000 deaths annually¹. Many of these deaths–up to 90%–are associated with metastatic CRC¹. Cancer cell detachment and migration that leads to metastasis is preceded by several changes in protein expression, a transition called the epithelial-to-mesenchymal transition, or EMT². A number of changes in non-coding RNAs are implicated in cancer. One well studied association for CRC is increased expression of H19 lncRNA that is associated with worse prognoses²^–⁴. H19 lncRNA competitively binds to and inhibits miR29b, among other members of the miR29 family⁴.  One of the roles of the miR29 family may be to attenuate DNA methyltransferases, preventing deactivation of certain genes,  and therefore keep expression of proteins like WIF-1 sufficiently high to prevent overactive Wnt/Beta-Catenin signaling⁵^,⁶. Methods. Cox multivariate analysis was used to correlate levels of H19 lncRNA in CRC tissues from patients with TNM stage (p<0.05)². RNA-seq was used to measure levels of H19 lncRNA in metastatic versus non-metastatic CRC cells in vitro¹. RNA immunoprecipitation (RIP) and affinity pulldown assays were used to determine miRNA targets of H19⁶. Western blots and qPCR were used to measure expression changes of various genes and proteins involved in EMT and Wnt/Beta catenin pathway regulation that changed when  miR29b-3p levels increased⁵^,⁷. Results. H19 was found to be the most highly upregulated lncRNA in metastatic CRC cells compared to control non-metastatic CRC cells  in vitro¹. RNA immunoprecipitation (RIP) and affinity pulldown assays demonstrated that H19 lncRNA and miR-29b-3p are capable of binding each another, suggesting that H19 is a sink for miR-29b-3p⁷. Increasing levels of miR29 by transfection increased levels of Wnt inhibitory factor 1 as shown by Western blots⁵. Fibroblasts treated with a miR29-b analog had more migratory potential than fibroblasts treated with a miR29-b inhibitor⁷. Conclusions. H19 binding of miR29b-3p can lead to a cascade of effects that contribute to dysregulation of the Wnt/Beta catenin pathway. This may be a key mechanism by which Wnt/Beta catenin signaling becomes overactivated in CRC. H19 may also play a key role in EMT. While there is a well-established link between H19 and CRC in literature, further study is required to ascertain downstream mechanisms by which H19 promotes tumorigenesis and metastasis.

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