Oncogenic Activation in Different Cancers

**31**

**Chapter 3**

**Abstract**

MicroRNAs (miRNAs) in

*Burcin Baran, Nazli-Mert Ozupek, Gizem Calibasi-Kocal* 

Colorectal cancer (CRC) is the third most common cancer in the world and third leading cause of cancer-related deaths in men and women as well. While early screening procedures and removal of small polyps improve the survival rates among the patients, there is still need for new diagnostic and therapeutic approaches for developing more effective treatments. MicroRNAs (miRNAs) are short noncoding RNA fragments, which involve in posttranscriptional regulation of gene expression, and they are shown to involve in tumorigenesis either targeting oncogenes or tumor suppressor genes. Based on the current studies, miRNAs are now suggested as potential biomarkers for CRC diagnosis, prognosis, and therapeutic responses. In this chapter, the latest findings on the role of miRNA in CRC in many aspects are reviewed: diagnosis (role of circular miRNAs in blood and miRNAs from tissue biopsies and their potential role in pathophysiology and diagnosis of CRC), prognosis (miRNAs related with metastasis, recurrence, and survival rates in CRC), and therapeutic responses (role of miRNAs both in chemotherapies and/or in targeted therapies in CRC). In conclusion, miRNAs are promising molecules for diagnosis, prognosis, and

**Keywords:** colorectal cancer, diagnosis, miRNA, prognosis, therapeutic response

MicroRNAs are a subgroup of small noncoding RNAs containing 18–25 nucleotides, and they do not carry any genetic information for protein expression. They regulate the posttranslational gene expression by binding 3′ untranslated region (UTR) of the target messenger RNA (mRNA). Approximately 30% of protein coding genes are regulated by miRNAs, and they have important roles in cellular functions including proliferation, differentiation, apoptosis, signaling, metabolism, and tumorigenesis. Due to their effect on crucial processes, miRNAs are significant modifiers of transcription and translation of both oncogenes and tumor suppressor proteins. Hence, some of them are classified as oncomiR and tumor suppressor

First miRNA, lin-4, was discovered in *Caenorhabditis elegans* in 1993, and it had role on the regulation of larval development by the repression of a nuclear protein encoded by *lin-14.* The second discovered miRNA, let-7, is expressed in late development and complementary to the 3′ UTR of the several genes including lin-14,

Colorectal Cancer

*and Yasemin Basbinar*

therapeutic responses of CRC.

miRNA in the cellular processes of tumor [1].

**1. Introduction**
