IADR Abstract Archives

MAPK and Smad1 Activation by Phosphophoryn

Background: The extracellular matrix (ECM) of dentin and bone provides spatial and temporal cues during tissue morphogenesis. Signals from the ECM are interpreted into cell fate changes via intracellular signaling networks. The non-collagenous protein, phosphophoryn (PP) is highly acidic and anionic and hypothesized to play a role in dentin biomineralization and also appears to have a signaling function. PP, a SIBLING protein, communicates with the cell via RGD/integrin interactions. Via the MAP kinase pathway, PP may initiate changes in gene expression and play a role in cell differentiation.

Objective: Investigate the RGD motif's role in PP's signaling and determine if additional pathways, other than the MAPK pathway, are involved.

Methods: Human adult mesenchymal stem cells (hMSCs) were treated with recombinant phosphophoryn (rPP). Western blot and immunohistochemical techniques were performed to determine if the Smad pathway is activated. Noggin was utilized to rule out the involvement of BMP-2 in Smad activation. siRNA was used to understand the pathways. QPCR analysis was performed to quantify gene expression following PP treatment. Significant differences among treatment groups were determined by a one-way ANOVA with Fisher's LSD post hoc test at a 95% confidence level.

Results: Our data suggest that PP could signal in an integrin-independent manner and in addition to the involvement of the MAPK pathway, PP also activates the Smad pathway. Furthermore crosstalk may occur between the MAPK and Smad signaling pathways during PP stimulation. PP directly activates Smad1 independently of BMP2. Activation of these signaling pathways resulted in transcriptional activity and regulation of target genes important for dentinogenesis/osteogenesis. Additionally, the role of post-translational modification, phosphorylation in particular, is important in regards PP's role.

Conclusion: PP may have a critical role in cell fate determination and biomineralization. The dual roles of PP highlight the importance of specialized extracellular matrix proteins of mineralized tissues.


AADR/CADR Annual Meeting
2006 AADR/CADR Annual Meeting (Orlando, Florida)
Orlando, Florida
2006
44
Mineralized Tissue
  • Jadlowiec, Julie  ( Carnegie Mellon University, Pittsburgh, PA, USA )
  • Li, Jinhua  ( University of Pittsburgh, Pittsburgh, N/A, USA )
  • Zhang, Xiaoyuan  ( University of Pittsburgh, Pittsburgh, PA, USA )
  • Piesco, Nicholas  ( University of Pittsburgh, Pittsburgh, PA, USA )
  • Campbell, Phil  ( Carnegie Mellon University, Pittsburgh, PA, USA )
  • Sfeir, Charles  ( University of Pittsburgh, Pittsburgh, PA, USA )
    • Oral Session
    Keynote Address and Osteogenesis/Dentinogenesis/Pathology
    03/08/2006