Regulation of desaturase expression in HL60 cells.

The expression of delta 5 desaturase (D5D), delta 6 desaturase (D6D) and delta 9 desaturase (D9D) was determined by RT-PCR in the human promyelocytic cell line HL60. During 72 h of culture with 10% FBS, D5D and D6D were upregulated 5 to 6-fold, whereas D9D approximately doubled. The addition of fatty acids (FAs) to the culture medium suppressed upregulation of all desaturases. N-3 and n-6 FA appeared to be more effective than n-9 or saturated FA. When FAs were added after 72 h, further upregulation during the next 24 h was suppressed for nearly all desaturases and FAs tested, except for D5D when oleic acid (OA) or stearic acid (SA) was added. In cells cultured with restricted amounts of FBS, desaturase expression increased with decreasing concentrations of FBS. Cellular FA content decreased by 60% in the neutral lipid fraction, whereas that of the phospholipid fraction decreased by 10% during 72 h of culture. The largest decrease occurred in the sum of n-3 and n-6 FA of the neutral lipid fraction, which was reduced by 83%, whereas the content of these FAs in the phospholipid fraction decreased by 32%. The results indicate that when the supply of FA to HL60 cells is limited, the intracellular content of n-3 and n-6 FA decreases and this leads to upregulation of the desaturases, particularly D5D and D6D. Since HL60 cells resemble human leukocytes, the results suggest that desaturase expression in leukocytes may be exploited as a biomarker for FA status.