Neural regulation of the formation of skeletal muscle phosphorylase kinase holoenzyme in adult and developing rat muscle

Abstract

Neural influences on the co-ordination of expression of the multiple subunits of skeletal muscle phosphorylase kinase and their assembly to form the holoenzyme complex, α % β % γ % δ % , have been examined during denervation and re-innervation of adult skeletal muscle and during neonatal muscle development. Denervation of the tibialis anterior and extensor digitorum longus muscles of the rat hindlimb was associated with a rapid decline in the mRNA for the γ subunit, and an abrupt decrease in γ-subunit protein. The levels of the α-and β-subunit proteins in the denervated muscles also declined rapidly, their time course of reduction being similar to that for the γ-subunit protein, but they did not decrease to the same extent. In contrast with the rapid decline in γ-subunit mRNA upon denervation, α-and β-subunit mRNAs stayed at control innervated levels for approx. 8-10 days, but then decreased rapidly. Their decline coincided very closely with the onset of re-innervation. Re-innervation of the denervated muscles, which occurs rapidly and uniformly after the sciatic nerve crush injury, produced an eventual slow and prolonged recovery of the mRNA for all three subunits and

Differentiation-dependent mechanisms of transcriptional regulation of the catalytic subunit of phosphorylase kinase

“…By 3 days after the change in medium the subunit proteins reach a stable level that is about 3-5 % of that of adult skeletal muscle [23]. Increases beyond that level, as occur in normal developing skeletal muscle, requires neural input, as occur with innervation during normal muscle development [7]. As illustrated for C2C12 cells, induced differentiation from myoblasts to myotubes under the conditions used in the present study occurs with a prompt induction of the PhK γ mRNA (Figure 2).…”

“…Several sets of studies indicate that there is a very close co-ordination of expression of the multiple subunits, such that the γ subunit is not expressed in the absence of its regulatory subunits. During normal skeletal-muscle development [7], muscle degeneration and subsequent regeneration following bupivacaine-induced degeneration [8], and the reinnervation of muscle following nerve transection [9] the fully composed holoenzyme is altered dramatically in amount, but the free γ subunit is never produced. It is apparent that the transcription and translation of the α, β and δ subunits is dictated by that of the γ subunit.…”

“…and mRNA levels during normal skeletal-muscle development [7], in regenerating muscle following bupivacaine-induced muscle degeneration [8] and during the process of re-innervation of muscle following nerve transection [7,9]. In all circumstances when the total level of PhK increased, there was a concomitant expression of the catalytic γ subunit and its regulatory subunits with the result that holoezyme formation accompanied subunit expression ensuring control of γ subunit catalytic activity.…”

“…When PhK activity was markedly reduced by nerve transection, the initial response was a decline in both γ subunit protein and mRNA levels, followed, after a brief delay, by a similar decrease in the levels of α and β subunit proteins. Interestingly, there was an extended delay before the levels of the α and β subunit mRNAs decline, thus maintaining a greater capacity for α and β subunit formation and ensuring that the γ subunit is only present as part of the holoenzyme [7]. The level of PhK holoenzyme, and its constituent subunits, appears to be governed by the transcriptional regulation and expression of the γ subunit.…”

Muscle glycogenosis with low phosphorylase kinase activity: mutations in PHKA1, PHKG1 or six other candidate genes explain only a minority of cases

“…In rat muscle, Phk activity and protein levels have been shown to drop deeply following experimental degeneration 56 or denervation. 57 To avoid a biochemical misdiagnosis of muscle Phk deficiency, special care may be necessary in the timing, site choice and specimen handling of muscle biopsies, and other enzyme deficiencies that can cause a similar glycogenosis should be comprehensively excluded even if low Phk and phosphorylase-a activities are measured. It may also be advisable to assay Phk routinely at pH 6.8 and 8.2, because Phk activity is markedly pH-dependent and the pH 6.8/8.2 activity ratio reflects the enzyme's molecular status.…”