RESUMEN
Cholesterol is an important lipid in higher organisms, and its concentration must be maintained in narrow limits depending of the cell needs. An excess of dietary cholesterol can lead to serious health problems, however, if consumption of this lipid is restricted in the diet, cells have the capacity to synthesize it. For the synthesis of cholesterol, the cell uses a family of proteins named sterol regulatory element binding proteins (SREBP's), that are transcriptional factors involved in the control of expression of genes of cholesterol and fatty acids synthesis. SREBP's regulate gene transcription by binding to cis-acting elements denominated sterol regulatory elements (SRE-1). SREBP's are localized in the endoplasmic reticulum, but in the event that the cell needs to synthesize cholesterol, the NH2-terminal portion of these proteins is cleaved by two specific proteases, and then travels into the nucleus to function as transcriptional factor. The present review shows the details of the mechanism that the cell uses to regulate cholesterol biosynthesis by the SREBP's, and its potential metabolic implications.