Low‐density lipoprotein receptor‐related protein mediates in PC12 cell cultures the inhibition of nerve growth factor‐promoted neurite outgrowth by pregnancy zone protein and α₂‐macroglobulin

Abstract

Human pregnancy zone protein (PZP) is a major pregnancy-associated plasma protein closely related to human alpha(2)-macroglobulin (alpha(2)M). It has been demonstrated that monoamine-activated forms of human and rat alpha(2)M and rat alpha(1)M can bind to TrkA and, respectively, inhibit and stimulate NGF-promoted neurite outgrowth, Trk phosphorylation, and intracellular signal transduction in PC12 cells. However, the effect of PZP on neurons is unknown, and the molecular mechanism of neuroinhibition by monoamine-activated alpha(2)M is still unclear. In this report, we show that methylamine-activated PZP (MA-PZP), like MA-alpha(2)M, inhibits in a dose-dependent way the NGF-promoted neurite extension and TrkA phosphorylation in PC12 cells. On the other hand, normal PZP (N-PZP) had little or no effect. In addition, the inhibitory effect of activated alpha-macroglobulins (alphaMs) was reversible upon its removal from the cell culture. In addition, PZP, as well as alpha(2)M, is neuroinhibitory without being directly cytotoxic. It is known that the activated alphaMs bind to the multiligand receptor termed low-density lipoprotein receptor-related protein (LRP) and that the receptor-associated protein (RAP) specifically blocks uptake of all known LRP ligands. To investigate the potential role of LRP in neuromodulation by activated PZP/alpha(2)M, the effect of RAP on the neuroinhibitory activities of these alphaMs was also studied. Data presented here show that RAP blocked the neurite- and Trk-inhibitory activities of both MA-PZP and MA-alpha(2)M, whereas RAP itself had no neuromodulatory effect. Hence, we conclude that these data suggest that the LRP receptor and its alphaM ligands may play a role in regulating Trk receptors.

Low-density Lipoprotein Receptor-related Protein 1 (LRP1)-dependent Cell Signaling Promotes Axonal Regeneration

“…A previous report suggested that ␣2-macroglobulin may directly bind Trks independently of LRP1 (48). However, our results and others (23) indicate that structurally diverse LRP1 ligands, including matrix metalloproteinase 9-PEX and RBD, all activate Trks, A,and ERK1/2 and that these actions are blocked by RAP.…”

Activated α2‐Macroglobulin Induces Mesenchymal Cellular Migration Of Raw264.7 Cells Through Low‐Density Lipoprotein Receptor‐Related Protein 1

“…Alpha 2 M was purified from human plasma following a procedure described previously [Chiabrando et al, ]. The activated form of α 2 M (α 2 M*) was generated by incubating purified native α 2 M with 200 mM methylamine‐HCl for 6 h at pH 8.2, as reported previously [Chiabrando et al, ]. The α 2 M* but not the native α 2 M can specifically interact with LRP1 [Chu and Pizzo, ; Sanchez et al, ].…”

A Pro-Nerve Growth Factor (proNGF) and NGF Binding Protein, α2-Macroglobulin, Differentially Regulates p75 and TrkA Receptors and Is Relevant to Neurodegeneration Ex Vivo and In Vivo

“…A protein present in serum and in tissues, ␣ 2 -macroglobulin (␣ 2 M), has been reported as an NGF binding protein: ␣ 2 M can bind to mature NGF (dissociation constant [K d ] of 172 nM) making stable ␣ 2 M-NGF complexes (14). ␣ 2 M inhibits NGF bioactivity (14)(15)(16), an effect interpreted as neutralization by ␣ 2 M sequestration of NGF (15,16). However, this interpretation relies on the presumed absence of TrkA binding by ␣ 2 M-NGF complexes or on actions mediated by the low-density lipoprotein receptor-related protein 1 (LRP1) (17), the cognate receptor for ␣ 2 M, but these have not been studied.…”