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Hydrophobic Membrane Translocating Sequence Peptides 121
FIGURE 6.1 (Color Figure 6.1 follows p. 14.) The effect of kFGF MTS-Grb2 translocation
on growth factor signaling. (A) The activated EGF receptor is phosphorylated and subsequently
bound by the Grb2 SH2 domain, which in turn recruits Sos and Ras molecules.
Activation of Ras leads to cellular responses including mitogenesis. (B) Introduction of the
kFGF MTS-Grb2 conjugate results in the binding of this conjugate to the activated EGF
receptor and inhibition of binding of native Grb2. Thus, Sos and Ras are not activated and
cellular signaling is inhibited.
to proteolysis; the peptide blocked the nuclear import of NF-κB and it was determined
that NF-κB plays an important role in acute inflammatory disease models.
The minimal peptide that inhibits Stat3 signaling has been identified by coupling
phosphorylated peptides to the kFGF MTS. 79 Constitutive activation of Stat3 frequently
accompanies various human malignancies; therefore, this peptide inhibitor
is being investigated as a peptidomimetic for drug design. Croce and co-workers
successfully synthesized a cell-permeant inhibitor of the Ca 2+ -activated protease
calpain by assembling a peptide containing the kFGF MTS and the minimal inhibitory
sequence (24 residues) of the known calpain inhibitor, calpastatin. 80
The ability of kFGF MTS to aid in translocation of large proteins has also been
demonstrated. 36 A 12-residue MTS (AAVLLPVLLAAP) derived from the 16-residue
h-region of the signal sequence of kFGF 81 was expressed adjacent to a fusion protein
comprising Schistosoma japonicum glutathione S-transferase and the Grb2 SH2
domain, 82 resulting in a 41-kDa MTS-protein conjugate. The protein was found to
be imported into every cell on a culture dish and the amount of protein taken up by
each cell was up to several million copies, depending on extracellular concentration
and incubation time. Exposure of cells to the MTS-protein conjugate resulted in
inhibition of EGF-induced intracellular signaling and mitogenesis, as shown in
Figure 6.1.