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In vitro functional studies of naturally occurring pathogenic PRKAR1A mutations that are not subject to nonsense mRNA

Elizabeth L Greene1, Anelia D Horvath, Maria Nesterova

  • 1Section on Endocrinology & Genetics, Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.

Human Mutation
|February 5, 2008
PubMed

Insights

Seven PRKAR1A mutations cause Carney complex by producing a functional, but overactive, RIalpha protein. This suggests altered protein function, not just loss, drives tumorigenesis.

Area of Science:

  • Genetics
  • Molecular Biology
  • Endocrinology

Background:

  • Germline mutations in PRKAR1A, encoding the RIalpha subunit of protein kinase A (PKA), are linked to primary pigmented nodular adrenocortical disease (PPNAD) and Carney complex (CNC).
  • Most disease-causing PRKAR1A mutations result in non-functional proteins due to nonsense-mediated mRNA decay (NMD).
  • The role of expressed mutant RIalpha protein in tumorigenesis remains less understood.

Purpose of the Study:

  • To identify and characterize PRKAR1A mutations that escape NMD and result in expressed mutant RIalpha protein.
  • To investigate the functional consequences of these expressed mutations on PKA activity.
  • To determine if altered PRKAR1A protein function contributes to tumorigenesis in CNC.

Main Methods:

  • Identification of seven novel PRKAR1A mutations in patients with PPNAD, CNC, or sporadic tumors.
  • Analysis of mRNA decay pathways to confirm mutations escape NMD.
  • Assessment of PKA activity in cells expressing the identified mutant RIalpha proteins.

Main Results:

  • Seven PRKAR1A mutations (p.Ser9Asn, p.Glu60_Lys116del, p.Arg74Cys, p.Arg146Ser, p.Asp183Tyr, p.Ala213Asp, p.Gly289Trp) were identified.
  • These mutations lead to the expression of mutant RIalpha proteins, indicating they evade NMD.
  • All expressed mutant RIalpha proteins demonstrated increased PKA activity, likely due to reduced binding to cAMP or the catalytic subunit.

Conclusions:

  • Altered PRKAR1A protein function, not solely haploinsufficiency, can elevate PKA activity and contribute to CNC-associated tumorigenesis.
  • Expressed mutant PRKAR1A proteins can be detrimental, potentially more so than complete loss of function (allelic loss).
  • These findings highlight the importance of functional protein expression in the pathogenesis of PKA-related endocrine disorders.

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