Phosphofructokinase (PFK) regulation of glycolysis in skin

Differentiation-dependent increases in lactate dehydrogenase activity and isoenzyme expression in rabbit corneal epithelial cells

Lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) activities were studied during corneal epithelial growth and differentiation in cell culture. LDH and G-6-PDH activities increased up to 60 and 150-fold, respectively, when corneal epithelial cells constituted a differentiated four to five layered epithelium; these increases showed a similar time-course to the expression of K3 keratin. Immunostaining experiments showed that in growing colonies, LDH staining is stronger in those cells that are K3 positive; in contrast, in confluent four to five layered epithelia LDH and K3 were located in all cell layers, similar to the pattern found in frozen sections from rabbit central cornea. During growth and differentiation, the LDH isoenzyme set from corneal epithelial cells did not change; and it was different from those observed in cultured conjunctival, esophageal and epidermal cells. The augment in LDH activity was due to a 25-fold increase in the LDH-H mRNA and a 12-fold augment in LDH-M mRNA. A computer-assisted search led to identify AP2 and Sp1 binding sites in the LDH and G-6-PDH promoters, suggesting that their expression might share common regulatory mechanisms with the regulation of the differentiation-linked keratins. It is proposed that LDH may be an early marker of corneal epithelial differentiation, and its isozyme pattern could be distinctive from other epithelial cell lineages.

Enhancement in the activities of mouse epidermal glucose-6-phosphate dehydrogenase, hexokinase, phosphofructokinase, and pyruvate kinase by 12-O-tetradecanoyl-phorbol-13-acetate

The active ingredient in the tumor-promoting croton oil, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), was shown to increase the activity of mouse skin epidermal glucose-6-phosphate dehydrogenase (+84%), hexokinase (+100%), phosphofructokinase (+158%), and pyruvate kinase (+101%). This increase in activity of these key enzymes of glucose metabolism occurred 2-8 h after TPA application and was due to a net increase in the enzyme content. This increase in the activity of the glycolytic enzymes, as well as the reported TPA-induced increase in the synthesis of RNA and DNA and cell proliferation, suggest that activation of the glycolytic pathway may be involved in the carcinogenic effects of tumor promoters.

The effects of catecholamine and related compounds on the adenyl cyclase system in the epidermis

The effect of various hormones and drugs on the adenyl cyclase system of pig and human epidermal slices was studied in vitro. Adrenaline and isoproterenol in the presence of theophylline increased the epidermal cyclic AMP level 20-fold in 5 min. Noradrenaline also stimulated cyclic AMP accumulation but to a much lesser degree. The adrenaline stimulation was marked even in the absence of the phosphodiesterase inhibitor, theophylline. Theophylline potentiated the effect of adrenaline at the concentration of 2-10 mM although theophylline alone did not elevate the cyclic AMP level significantly. The Km for adrenaline stimulation of the adenyl cyclase system of pig epidermis was 7-7 X 10(-7) M. A beta-adrenergic antagonist, propranolol, markedly inhibited the adrenaline stimulation while alpha-antagonists, phentolamine or priscoline, showed little effect. The results are in accord with the view that the epidermis possesses an active adenyl cyclase system with beta-adrenergic receptors.

Micro-determination of cyclic AMP levels in human epidermis, dermis and haif follicles

In order to study the biological and possible pathological roles of cyclic adenosine 3',5'-monophosphate (cyclic AMP) in the skin, it is mandatory to measure cyclic AMP in 50-100 mug of microdissected epidermis, dermis or appendages. In the present study, we offer a method of extracting cyclic AMP from less than 100 mug of tissue, removing contaminating nucleotides and scaling down Gilman's method to fit the analysis of small amounts of tissue. Cyclic AMP levels in the dermis, epidermis, and hair follicles (bulbs) were approximately 1, 2 and 3-5 pmols/mug dry weight tissue respectively. This procedure is applicable to the measurement of cyclic AMP levels in limited foci of healthy or diseased skin.

Cyclic AMP in skin: effects of acute ischaemia

The cyclic adenosine 3',5'-monophosphate (cyclic AMP) content of pig skin was measured several seconds to minutes after removal of the skin from the body. It increased very rapidly, reached a maximum by 2 min after removal (4 times higher than the initial level), then decreased very slowly. Propranolol injected into the animal before or added after the removal of the skin did not suppress this phenomenon. The practical significance of this finding (increase of cyclic AMP level in skin after ischaemia) is obvious-in order to measure cyclic AMP level in vivo, the sample must be frozen immediately to avoid an 'artificial' increase in cyclic AMP.