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Protein kinase C inhibitors alter neurotensin receptor binding and function in prostate cancer PC3 cells

Robert E Carraway1, Sazzad Hassan, Paul R Dobner

  • 1Department of Cellular and Molecular Physiology, University of Massachusetts Medical School, 55 Lake Avenue North Worcester, MA, 01655, United States. Robert.carraway@umassmed.edu

Regulatory Peptides
|March 4, 2008
PubMed

Insights

Protein kinase C (PKC) regulates neurotensin (NT) receptors in prostate cancer cells. Conventional PKCs suppress NT receptor function, while novel PKCs maintain NT signaling, suggesting dual regulatory roles.

Area of Science:

  • Molecular Pharmacology
  • Cell Signaling
  • Cancer Research

Background:

  • Prostate cancer PC3 cells exhibit constitutive protein kinase C (PKC) activity.
  • This endogenous PKC activity normally suppresses neurotensin (NT) receptor function.
  • PKC activity can be modulated by inhibitors and activators like phorbol myristic acid (PMA).

Purpose of the Study:

  • To investigate the role of protein kinase C (PKC) in regulating neurotensin (NT) receptor function in PC3 prostate cancer cells.
  • To elucidate the distinct mechanisms employed by conventional and novel PKC isoforms.
  • To determine if NT receptor function is subject to homologous regulation by PKC.

Main Methods:

  • Assessment of endogenous PKC activity using a cell-based PKC substrate phosphorylation assay.
  • Treatment with various PKC inhibitors (staurosporine, Go-6976, etc.) and PMA.
  • Measurement of NT receptor binding, NT-induced inositol phosphate (IP) formation, and PKC isoform expression (alpha, betaI, delta, epsilon).
  • PKC downregulation and knockdown studies.
  • Scatchard analysis to determine receptor affinity and number.

Main Results:

  • PKC inhibitors enhanced NT receptor binding and NT-induced IP formation, while PMA inhibited these functions.
  • Conventional PKCs (alpha, betaI) were implicated in suppressing NT receptor binding and signaling.
  • Novel PKCs (delta, epsilon) were found to inhibit NT-induced IP formation, particularly at higher inhibitor concentrations or via knockdown.
  • PKC modulation affected NT receptor affinity, not receptor number or internalization.
  • The inhibition of IP formation by novel PKCs was specific to NT and not observed with bombesin.

Conclusions:

  • PKC heterologously regulates NT receptor function through distinct mechanisms involving conventional and novel isoforms.
  • Conventional PKCs inhibit NT receptor binding and signaling.
  • Novel PKCs maintain the ability of NT to stimulate phospholipase C (PLC), but can also inhibit NT-induced IP formation at higher concentrations.
  • The NT receptor may also be subject to homologous regulation by PKC, as NT binding can activate PKC.

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