Developmental regulation of alternatively spliced acetyl-CoA carboxylase-alpha mRNAs encoding isozymes with or without an eight amino acid domain upstream of the Ser-1200 phosphorylation motif in the mammary gland

Expression of a variant acetyl-CoA carboxylase-alpha (ACC-alpha) mRNA encoding an isozyme either comprising (+24nt) or lacking (Delta24nt) an eight amino acid domain proximal to the Ser-1200 phosphorylation motif has been investigated in ovine and rat mammary tissue throughout pregnancy and lactation. The ratio of the Delta24nt mRNA: +24nt mRNA in ovine tissues varied from 0.1-0.25 (spleen, lung, muscle, heart, adipose tissue, brain) to 0.6-0.8 (pancreas, liver, kidney) to approximately 5.0 (lactating mammary gland). The sixfold increase in total ACC-alpha mRNA expression in mammary gland during lactation was due entirely to a tenfold increase in the level of the Delta24nt species as the level of expression of the +24nt species remained unaltered between pregnancy and lactation. This mode of expression of the +24nt and Delta24nt mRNAs was similar in rat mammary gland. Between day 20 of pregnancy and day 4 of lactation the ratio of the Delta24nt : +24nt mRNA increased from 2:1 to 10-20:1. Forced involution reduced the ratio of the two mRNAs to levels observed throughout pregnancy. Treatment of lactating rats with bromocryptine reduced the ratio of the Delta24nt : +24nt mRNA to relative levels observed after forced involution, suggesting that the exonic splicing responsible for the generation of the two mRNA isoforms is prolactin responsive.

Download Full-text

Studies on acetyl-CoA carboxylase and fatty acid synthase from rat mammary gland and mammary tumours

Biochemical Journal ◽

10.1042/bj2080443 ◽

1982 ◽

Vol 208 (2) ◽

pp. 443-452 ◽

Cited By ~ 2

Author(s):

P M Ahmad ◽

D S Feltman ◽

F Ahmad

Keyword(s):

Mammary Gland ◽

Fatty Acid ◽

Fatty Acid Synthase ◽

Mammary Tissue ◽

Acetyl Coa Carboxylase ◽

Lipogenic Enzymes ◽

Acetyl Coa ◽

Rat Mammary Gland ◽

Mammary Gland Differentiation ◽

Mammary Adenocarcinomas

The activities of two lipogenic enzymes, acetyl-CoA carboxylase and fatty acid synthase, were determined in two transplantable mammary adenocarcinomas (13762 and R3230AC) carried by non-pregnant, pregnant and lactating rats, and in mammary tissue of control animals (non-tumour-carrying) of comparable physiological states. During mammary-gland differentiation of control or tumour-carrying animals, the activities of acetyl-CoA carboxylase and fatty acid synthase in the lactating gland increased by about 40-50-fold over the values found in non-pregnant animals. On the other hand, in tumours carried by lactating dams there were only modest increases (1.5-2-fold) in acetyl-CoA carboxylase and fatty acid synthase compared with the neoplasms carried by non-pregnant animals. On the basis of the Km values for different substrates and immunodiffusion and immunotitration data, the fatty acid synthase of neoplastic tissues appeared to be indistinguishable from the control mammary-gland enzyme. However, a comparison of the immunotitration and immunodiffusion experiments indicated that the mammary-gland acetyl-CoA carboxylase might differ from the enzyme present in mammary neoplasms.

Download Full-text

Purification and Physicochemical Properties of Fatty Acid Synthetase and Acetyl-CoA Carboxylase from Lactating Rabbit Mammary Gland

European Journal of Biochemistry ◽

10.1111/j.1432-1033.1978.tb12719.x ◽

1978 ◽

Vol 92 (1) ◽

pp. 25-34 ◽

Cited By ~ 39

Author(s):

D. Grahame HARDIE ◽

Philip COHEN

Keyword(s):

Mammary Gland ◽

Fatty Acid ◽

Physicochemical Properties ◽

Fatty Acid Synthetase ◽

Acetyl Coa Carboxylase ◽

Acetyl Coa

Download Full-text

Growth-hormone-prolactin interactions in the regulation of mammary and adipose-tissue acetyl-CoA carboxylase activity and gene expression in lactating rats

Biochemical Journal ◽

10.1042/bj2850469 ◽

1992 ◽

Vol 285 (2) ◽

pp. 469-475 ◽

Cited By ~ 27

Author(s):

M C Barber ◽

M T Travers ◽

E Finley ◽

D J Flint ◽

R G Vernon

Keyword(s):

Adipose Tissue ◽

Mammary Gland ◽

Serum Prolactin ◽

Acetyl Coa Carboxylase ◽

Acetyl Coa ◽

Carboxylase Activity ◽

Total Enzyme Activity ◽

Mrna Concentration ◽

Total Enzyme ◽

Activation Status

The factors and mechanisms responsible for the reciprocal changes in lipogenesis in rat mammary gland and adipose tissue during the lactation cycle have been investigated. Lactation decreased the activation status and mRNA concentration of acetyl-CoA carboxylase in adipose tissue. Litter removal decreased the mRNA concentration of acetyl-CoA carboxylase in the mammary gland and increased the enzyme's mRNA concentration and activation status in adipose tissue. Lowering serum prolactin concentration in lactating rats decreased the amount of mammary acetyl-CoA carboxylase mRNA and increased that of adipose tissue, and increased the activation status of the enzyme in adipose tissue. Decreasing serum growth hormone (GH) alone had little effect on acetyl-CoA carboxylase in lactating rats, although it did lower pup growth rate and serum concentration of insulin-like growth factor-I. Lowering serum GH concentration exacerbated the effects of decreasing serum prolactin on mammary-gland (but not adipose-tissue) acetyl-CoA carboxylase mRNA and further increased the rise in activation status of the adipose-tissue enzyme induced by decreasing serum prolactin. Changes in acetyl-CoA carboxylase mRNA in both mammary and adipose tissue were paralleled by changes in total enzyme activity except after litter removal, when there was a disproportionately large decrease in total enzyme activity of the mammary gland. Thus prolactin has a major and GH a minor role in the regulation of acetyl-CoA carboxylase activity during lactation. Changes in mammary activity in response to prolactin and GH are primarily due to alterations in gene transcription, whereas adaptation in adipose tissue involves both changes in gene transcription and activation status.

Download Full-text

Regulation of acetyl-CoA carboxylase in rat mammary gland. Effects of starvation and of insulin and prolactin deficiency on the fraction of the enzyme in the active form in vivo

Biochemical Journal ◽

10.1042/bj2040273 ◽

1982 ◽

Vol 204 (1) ◽

pp. 273-280 ◽

Cited By ~ 17

Author(s):

Elizabeth M. McNeillie ◽

Victor A. Zammit

Keyword(s):

Mammary Gland ◽

Enzyme Activities ◽

Enzyme Concentration ◽

Acetyl Coa Carboxylase ◽

Initial Activity ◽

Acetyl Coa ◽

Activity Ratios ◽

Rat Mammary Gland ◽

Rate Limiting

The ‘initial’ (I), endogenous phosphatase-activated (A) and citrate-activated (C) activities of acetyl-CoA carboxylase were measured in mammary-gland extracts of pregnant and lactating rats. There was a 10-fold increase in the A and C enzyme activities in the transition from early to peak lactation [cf. data of Mackall & Lane (1977) Biochem. J.162, 635–642], but there was no significant increase in the ratio of the initial activity to the A and C activities of the enzyme. Starvation (24h) or short-term (3h) streptozotocin-induced diabetes both resulted in a 40% decrease in I/A and I/C activity ratios. In starvation this was accompanied by a decrease in the absolute values of the A and C activities such that the initial activity in mammary glands of starved animals was 45% that in glands from fed animals. Insulin treatment of starved or diabetic animals 60min before killing increased the I activity without affecting the A or C enzyme activities. Removal of the pups for 24h from animals in peak lactation (weaning) resulted in a marked but similar decrease in all three activities such that, although the initial activity was only 10% of that in suckled animals, the I/A and I/C activity ratios remained high and unaltered. Inhibition of prolactin secretion by injection of 2-bromo-α-ergocryptine gave qualitatively similar results to those during weaning. Simultaneous administration of ovine prolactin completely prevented the effects of bromoergocryptine. It is suggested that the initial activity of acetyl-CoA carboxylase in rat mammary gland is regulated by at least two parallel mechanisms: (i) an acute regulation of the proportion of the enzyme in the active state and (ii) a longer-term modulation of enzyme concentration in the gland. Insulin appeared to mediate its acute effects through mechanism (i), whereas prolactin had longer-term effects on enzyme concentration in the gland. A comparison of initial enzyme activities (I) obtained in the present study with rates of lipogenesis measured in vivo [Agius & Williamson (1980) Biochem. J.192, 361–364; Munday & Williamson (1981) Biochem. J.196, 831–837] gave good agreement between the two sets of data for all conditions studied except for 24h-starved and streptozotocin-diabetic animals. It is suggested that acetyl-CoA carboxylase activity is rate-limiting for lipogenesis in the mammary gland in normal, fed, suckled or weaned animals but that in starved and short-term diabetic animals changes in the activity of the enzyme by covalent modification alone may not be sufficient to maintain the enzyme in its rate-limiting role.

Download Full-text