Evidence that muscle cells do not express the histidine-rich glycoprotein associated with AMP deaminase but can internalise the plasma protein

Abstract

Histidine-rich glycoprotein (HRG) is synthesized by liver and is present at relatively high concentration in the plasma of vertebrates. We have previously described the association of a HRG-like molecule to purified rabbit skeletal muscle AMP deaminase (AMPD). We also provided the first evidence for the presence of a HRG-like protein in human skeletal muscle where a positive correlation between HRG content and total determined AMPD activity has been shown. In the present paper we investigate the origin of skeletal muscle HRG. The screening of a human skeletal muscle cDNA expression library using an anti-HRG antibody failed to reveal any positive clone. The RT-PCR analysis, performed on human skeletal muscle RNA as well as on RNA from the rhabdomyosarcoma (RD) cell line, failed to show any mRNA specific for the plasma HRG or for the putative muscle variant. When the RD cells were incubated with human plasma HRG, a time-dependent increase of the HRG immunoreactivity was detected both at the plasma membrane level and intracellularly. The internalisation of HRG was inhibited by the addition of heparin. The above data strongly suggest that skeletal muscle cells do not synthesize the muscle variant of HRG but instead can actively internalise it from plasma.

Immunohistochemical localization of histidine-rich glycoprotein in human skeletal muscle: preferential distribution of the protein at the sarcomeric I-band

“…Moreover, in a study on the origin of skeletal muscle HRG, we have demonstrated that muscle cells do not synthesize the protein but instead can actively internalize it from plasma, indicating for the first time that HRG can be carried to tissues via circulation (Sabbatini et al 2011). We have also described a positive correlation in human skeletal muscle between the content of HRG and the level of AMPD1 activity that it is known to be predominant in type IIB fast-twitch glycolytic fibers (Sabbatini et al 1999(Sabbatini et al , 2006.…”

New Insights into the Functions of Histidine-Rich Glycoprotein

“…The N-terminal sequence analysis of several tryptic peptides of this protein revealed a striking similarity to the fragments from rabbit plasma HRG. Further investigation, however, indicated that skeletal muscle cells do not synthesize the muscle variant of HRG but can instead actively internalize it from plasma (Sabbatini et al, 2011). Further investigation, however, indicated that skeletal muscle cells do not synthesize the muscle variant of HRG but can instead actively internalize it from plasma (Sabbatini et al, 2011).…”

Structure-function relationships in mammalian histidine-proline-rich glycoprotein

“…The role of HPRG as zinc chaperone 3.1. HPRG participates as zinc metallochaperone in the assembly and maintenance of skeletal muscle AMP deaminase According to Sabbatini et al [4], skeletal muscle cells do not transcribe HPRG but internalize the protein from serum. The percentage of internalized HPRG was reduced in the presence of heparin, indicating that heparin may compete with the cell surface GAGs in binding HPRG.…”

“…A protein very similar in sequence to HPRG co-purified with rabbit skeletal muscle AMP deaminase (AMPD) preparation [3]. It has been later demonstrated that the HPRG present in rabbit skeletal muscle is acquired from plasma since skeletal muscle cells do not synthesize the protein [4].…”