ASCL1-regulated DARPP-32 and t-DARPP stimulate small cell lung cancer growth and neuroendocrine tumour cell proliferation

  • Br J Cancer. 2020 Sep;123(5):819-832. doi: 10.1038/s41416-020-0923-6.
Sk Kayum Alam  1 ,  Li Wang  1 ,  Yanan Ren  1 ,  Christina E Hernandez  1 ,  Farhad Kosari  2 ,  Anja C Roden  3 ,  Rendong Yang  1  4 ,  Luke H Hoeppner  5  6
Affiliations
  • 1. The Hormel Institute, University of Minnesota, Austin, MN, USA.
  • 2. Department of Molecular Medicine, Mayo Clinic, Rochester, MN, USA.
  • 3. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA.
  • 4. Masonic Cancer Center, University of Minnesota, Minneapolis, MN, USA.
  • 5. The Hormel Institute, University of Minnesota, Austin, MN, USA. [email protected].
  • 6. Masonic Cancer Center, University of Minnesota, Minneapolis, MN, USA. [email protected].
PMID: 32499571 DOI: 10.1038/s41416-020-0923-6
Abstract

Background: Small Cell Lung Cancer (SCLC) is the most aggressive form of Lung Cancer, and new molecular insights are necessary for prognostic and therapeutic advances.

Methods: Dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32) and its N-terminally truncated splice variant, t-DARPP, were stably overexpressed or ablated in human DMS-53 and H1048 SCLC cells. Functional assays and immunoblotting were used to assess how DARPP-32 isoforms regulate SCLC cell growth, proliferation, and Apoptosis. DARPP-32-modulated SCLC cells were orthotopically injected into the Lungs of SCID mice to evaluate how DARPP-32 and t-DARPP regulate neuroendocrine tumour growth. Immunostaining for DARPP-32 proteins was performed in SCLC patient-derived specimens. Bioinformatics analysis and subsequent transcription assays were used to determine the mechanistic basis of DARPP-32-regulated SCLC growth.

Results: We demonstrate in mice that DARPP-32 and t-DARPP promote SCLC growth through increased Akt/Erk-mediated proliferation and anti-apoptotic signalling. DARPP-32 isoforms are overexpressed in SCLC patient-derived tumour tissue, but undetectable in physiologically normal lung. Achaete-scute homologue 1 (ASCL1) transcriptionally activates DARPP-32 isoforms in human SCLC cells.

Conclusions: We reveal new regulatory mechanisms of SCLC oncogenesis that suggest DARPP-32 isoforms may represent a negative prognostic indicator for SCLC and serve as a potential target for the development of new therapies.