Synthetic peptides derived from the stalk sequence of PC1 can stimulate signaling of stalkless PC1 CTF.
(A) Alignment of CTF stalk sequences from human (h) and mouse (m) PC1. CTFΔst has a 21-residue deletion from the N-terminal end of the stalk region. Arrow, GPS cleavage site. Non-identical residues shown in bolded blue. (B) Activation of the NFAT-luc reporter by transfected mCTF or mCTFΔst expression constructs shown relative to empty expression vector (ev) as means (+ standard deviation, SD) of 3 wells/construct from each of 7 independent experiments. (C) Representative Western blot of total cell lysates from one of the experiments in (B), probed with antisera A19 against mouse PC1 C-tail. ns, non-specific. (D) Summary of the total expression levels (means +SD) of CTFΔst relative to CTF from the experiments in (B). (E) Stalk peptide treatment of ev- or mCTFΔst-transfected cells. Sequences of stalk-derived peptides P7-P21 are shown. Graph represents the fold NFAT-luc activation for both eV- (gray bars) and CTFΔst- (blue bars) transfected cells relative to the CTFΔst control after 24 hr treatment with or without peptide. Results are the means (+SD) of 3 separate experiments, each with 3 wells/condition. *, p < 0.05; ***, p = 0.0001; ****, p < 0.0001. Analysis by 1-way ANOVA with Tukey-Kramer post-test.