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t-Darpp stimulates protein kinase A activity by forming a complex with its RI regulatory subunit

Dirk Theile1, Shuhui Geng2, Erin C Denny2

  • 1Department of Cancer Biology, City of Hope, 1500 East Duarte Road, Duarte, CA 91107, USA; Department of Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany.

Cellular Signalling
|September 5, 2017
PubMed

Insights

Truncated dopamine- and cAMP-regulated phosphoprotein (t-Darpp) confers trastuzumab resistance by activating protein kinase A (PKA). This occurs via t-Darpp binding to PKA regulatory subunit RI, disrupting RI-PKAc interaction, and requires T39 phosphorylation.

Area of Science:

  • Oncology
  • Molecular Biology
  • Biochemistry

Background:

  • Trastuzumab resistance in HER2-positive cancers is a significant clinical challenge.
  • The truncated form of dopamine- and cAMP-regulated phosphoprotein (t-Darpp) confers resistance to trastuzumab.
  • t-Darpp promotes resistance via sustained PI3K/Akt signaling and protein kinase A (PKA) activation, but the mechanism of PKA activation is unclear.

Purpose of the Study:

  • To elucidate the mechanism by which t-Darpp activates PKA.
  • To investigate the role of t-Darpp phosphorylation at T39 in PKA activation.
  • To identify potential therapeutic targets for overcoming t-Darpp-mediated drug resistance.

Main Methods:

  • Overexpression of wild-type t-Darpp and a T39A phosphorylation mutant in cancer cell lines.
  • Assessment of PKA activity and holoenzyme composition.
  • Evaluation of protein-protein interactions between t-Darpp and PKA subunits (PKAc, RI, RII).

Main Results:

  • Cells overexpressing wild-type t-Darpp exhibited elevated PKA activity and reduced association between PKA regulatory subunit RI and catalytic subunit PKAc.
  • The T39A phosphorylation mutant of t-Darpp did not lead to increased PKA activity or altered holoenzyme composition.
  • Wild-type t-Darpp directly associates with RI, sequestering it away from PKAc.

Conclusions:

  • t-Darpp phosphorylation at threonine 39 (T39) is critical for its ability to activate PKA.
  • t-Darpp activates PKA by binding to the RI subunit, thereby preventing its association with PKAc.
  • The interaction between t-Darpp and RI represents a potential druggable target to restore sensitivity to trastuzumab in resistant cancers.
Keywords:
Breast cancerProtein kinase ARegulatory subunit RIt-Darpp

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