Functional characterization of oleic (18:1) and arachiodonic (20:4) acid responsive regions of the rat Fatty Acid Synthase (FAS) gene

Type and amount of dietary fats affect several nutritionally related pathophysiologies (e.g., diabetes mellitus and cancer). This effect partially resides in the well known up and down regulation of gene transcription by fatty acids. One example of this is the polyunsaturated fatty acid suppression of FAS gene transcription. In order to map the DNA sequences of the FAS gene which are responsible for mediating the suppression of FAS transcription, the region of -9700 to +65bp of the FAS gene was cloned from a rat genomic library. Primary cultures of rat hepatocytes were transfected with a collection of chloramphenicol acetyl transferase (CAT) reporter constructs (from -9700 to -4606, -7383 to -4606, -4606 to -2700, and -265 to +65bp of the FAS gene) and examined for fatty acid responsivity. (n= 3-6 experiments per vector). The basal promoter region of -265 to +65bp was found to induce CAT expression twofold in response to 18:1, but was unaffected by 20:4. However, when the region from -7383 to -4606bp was ligated to the FAS basal promoter CAT expression (fmol/ug protein/ min) was 56 ±8, 61 ±10, and 21 ±3 for no fatty acids, 18:1 and 20:4, respectively. The 62% suppression of CAT activity elicited by 20:4 was localized to the region from -7383 to -6399bp. We conclude that the FAS gene transcription is regulated by fatty acids in two responsive sequences: one mediates a 20:4 silencer, and the other mediates a18:1 enhancer effect.