Preface

Most oncogenes are expressed as proto-oncogenes. They are involved in cell growth and proliferation or inhibition of apoptosis. If there are chemical, physical, or biological factors that cause mutations in such genes, these genes are mostly upregulated and cellular proliferation increases. In this case, they are termed "oncogenes." The cascade of events leading to proliferation usually predispose the cell to cancer. These genes are mutated and/or overexpressed at high levels in tumor cells. Tumors of the lung, breast, pancreas, and colon may display specific oncogenetic features. These tumors have been largely associated with exposure to environmental carcinogens and a variety of biological agents, including viruses. These carcinogens can induce specific genetic and epigenetic alterations (including modulation of DNA methylation, histone acetylation, and RNA expression) in these tissues, leading to aberrant functioning of oncogenes and tumor suppressor genes. On the other hand, microRNAs (miRNAs) are significant modifiers of transcription and translation of both oncogenes and tumor suppressor proteins, particularly in carcinogenesis. In the last 50 years, several oncogenes and miRNAs related to oncogenes have been identified in different types of human cancers. It is now clear that high expression of oncogenes, DNA damage response, and regulation of cell cycle are related to the circadian clock. There are several studies on cancer drugs that target the proteins encoded by oncogenes. In addition, the reversible nature of epigenetic modifications has led to the new field of "epigenetic therapy." Therefore, understanding the link between genetic alterations, epigenetic modifications, and expression of oncogenes can unravel the molecular targets for treating cancer. This book will mainly focus on the expressions of different oncogenes in breast, colon, and lung cancers. Moreover, the alterations in miRNAs in different types of cancers and the effects of the circadian clock on the expression of oncogenes in carcinogenesis will also be mentioned. Readers will mainly understand how the modulations and mutations in the expressions of oncogenes and related miRNAs lead to the promotion of carcinogenesis and how these alterations affect the carcinogenesis process in certain types of cancers. Moreover, readers will also gain knowledge of the relationship between the circadian clock and oncogenes.

> **Assoc. Prof. Dr. Pinar Erkekoglu** Editor, Hacettepe University, Faculty of Pharmacy, Department of Toxicology, Ankara, Turkey

**1**

Section 1

Introduction to Oncogene

Concept
