MeF2
Functional overload (OV) of
the rat plantaris muscle results in a fast to slow change in muscle phenotype
with induction of the slow contractile protein genes including myosin light
chain 2 slow (MLC2s). To identify potential cis-acting DNA sites regulating
MLC2s following ablation, plasmid constructs were transfected in vivo into
regenerating overloaded plantaris muscles. Activity of the 270bp promoter
(-270MLC2s) was increased in OV muscles at 28 days. Mutation of the MEF2 site
(-270MEF2) knocked out the overload-induced activity of the promoter. Mutation
of the Ebox (-270Ebox) resulted in an earlier induction with OV and mutation of
the CACC site (-270CACC) resulted in increased activity in the CON PLN with OV
induction detected by 21 days. These results demonstrate that the -270MLC2s
promoter contains the elements necessary for expression of MLC2s in
regenerating OV PLN. More importantly, mutation analysis of -270MLC2s promoter
demonstrates that mechanical loading induced expression shares some common
molecular mechanisms with slow nerve dependent model regulation. In these two
models of physiological induction of MLC2s, the CACC site acts as a repressor
region (on/off switch) and the MEF2 site acts to modulate quantitative
expression.
Two novel peptides that inhibit cathepsin B were isolated from a tryptic and chymotryptic hydrolysate of human serum albumin, and designated as Cabin-A1 and -A2. Cabin-A1 and -A2 were purified by reversed-phase HPLC and identified as Ser-Leu-His-Thr-Leu-Phe and Phe-Gln-Asn-Ala-Leu, respectively. These peptides correspond to f(65-70) and f(403-407) of human serum albumin. Human albutensin A (Ala-Phe-Lys-Ala-Trp-Ala-Val-Ala-Arg), which corresponds to f(210-218), was also isolated as a potent cathepsin B inhibitor. Synthetic Cabin-A1, -A2, and human albutensin A showed dose-dependent inhibition of cathepsin B, with K(i) values of 2.4, 290, and 3.8 microM, respectively.