Butyrate HeLa cells, effect

Figure 2. Effect of butyrate treatment on GM3 content of HeLa cells...

Exposure of HeLa cells to butyrate had no effect on the activity of GM3-sialidase when GM3 specifically labeled in the sialic acid residue was used as substrate (Fig. 3a). We were unable to detect any "ecto"-sialidase activity in either control or butyrate-treated cells (14) although others have postulated that such an enzyme is important in regulating plasma membrane gangliosides (15,16). In contrast, the activity of the specific sialyl transferase involved in GM3 biosynthesis increased over 20-fold following butyrate treatment (Fig. 3b). The effect was specific as activities of the other glycosphingolipid transferases that could be measured in HeLa cells were not altered in butyrate-treated cells (4,8,17). 

In recent work on CHO cells, it had been suggested that the effects of butyrate are mediated by cyclic AMP (18). We found, however, that cyclic AMP (2 mM), its mono- (1 mM and dibutyryl (0.5 mM) derivatives, theophylline and prostaglandins did not cause an elevation in si alyl transferase activity (1). Choleragen, which is a potent and persistant activator of adenylate cyclase (see below), also did not elevate sialyl transferase activity in HeLa cells (Table I) or alter cell morphology (unpublished observations). Thus, it is unlikely that these effects of butyrate are mediated by elevation of cyclic AMP levels. 

Figure 5. Effect of labeled and unlabeled choleragen concentrations on n5I-choleragen binding to control and butyrate-treated HeLa cells...

If GM1 is the choleragen receptor, then butyrate-treated cells should have an increase in GM1 content. This is demonstrated in Table IV. Although GM1 could not be detected in control HeLa cells, they would contain less than 1 pmol per mg protein based on the limits of the sensitivity of the analytical procedure (5). GM1 was quantitated in the butyrate-treated cells (28.5 pmol per mg protein) and this increase is similar to the 32-fold increase in toxin binding observed in cells from the same experiment. The delipidated residue contained less than 1% of the toxin binding found in intact cells (Table IV). In addition, removal of the cells from the culture dishes with trypsin as opposed to the mechanical scraping routinely used had no effect on 125I-cholera-gen binding to either control or butyrate-treated cells (5). 

Table IV. Effect of Sodium Butyrate on Choleragen Receptors and GM1 Content of HeLa Cells...

Increased GM3 content was also observed in another strain of HeLa exposed to butyrate but not in butyrate-treated normal human fibroblasts (experiments in collaboration with E. Stanbridge, University of California at Irvine and R. 0. Brady, NINCDS). Butyrate appeared to have similar effects on GM3 biosynthesis in KB cells, another human carcinoma-derived cell line (20). Butyrate-treated KB cells had 9-fold elevated levels of sialyl transferase activity. In contrast, butyrate as well as dibutyryl-... 

Butyrate appears to have its most profound effects on neoplastic cells such as HeLa in addition to morphological and biochemical differentiation, the fatty acid inhibits cell growth (2). Previous studies have established a correlation between decreased ganglioside synthesis and malignant transformation (43-46). Transformed baby hamster kidney and newborn rat kidney cells exhibited a loss of GM3 and sialyl transferase activity (43,44). 

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