Faculty Collaboration Database

Wild-type Kras expands and exhausts hematopoietic stem cells. JCI Insight 2018 Jun 07;3(11)

Date

06/08/2018

Pubmed ID

29875320

Pubmed Central ID

PMC6124423

DOI

10.1172/jci.insight.98197

Scopus ID

2-s2.0-85056627323 (requires institutional sign-in at Scopus site)   12 Citations

Abstract

Oncogenic Kras expression specifically in hematopoietic stem cells (HSCs) induces a rapidly fatal myeloproliferative neoplasm in mice, suggesting that Kras signaling plays a dominant role in normal hematopoiesis. However, such a conclusion is based on expression of an oncogenic version of Kras. Hence, we sought to determine the effect of simply increasing the amount of endogenous wild-type Kras on HSC fate. To this end, we utilized a codon-optimized version of the murine Kras gene (Krasex3op) that we developed, in which silent mutations in exon 3 render the encoded mRNA more efficiently translated, leading to increased protein expression without disruption to the normal gene architecture. We found that Kras protein levels were significantly increased in bone marrow (BM) HSCs in Krasex3op/ex3op mice, demonstrating that the translation of Kras in HSCs is normally constrained by rare codons. Krasex3op/ex3op mice displayed expansion of BM HSCs, progenitor cells, and B lymphocytes, but no evidence of myeloproliferative disease or leukemia in mice followed for 12 months. BM HSCs from Krasex3op/ex3op mice demonstrated increased multilineage repopulating capacity in primary competitive transplantation assays, but secondary competitive transplants revealed exhaustion of long-term HSCs. Following total body irradiation, Krasex3op/ex3op mice displayed accelerated hematologic recovery and increased survival. Mechanistically, HSCs from Krasex3op/ex3op mice demonstrated increased proliferation at baseline, with a corresponding increase in Erk1/2 phosphorylation and cyclin-dependent kinase 4 and 6 (Cdk4/6) activation. Furthermore, both the enhanced colony-forming capacity and in vivo repopulating capacity of HSCs from Krasex3op/ex3op mice were dependent on Cdk4/6 activation. Finally, BM transplantation studies revealed that augmented Kras expression produced expansion of HSCs, progenitor cells, and B cells in a hematopoietic cell-autonomous manner, independent from effects on the BM microenvironment. This study provides fundamental demonstration of codon usage in a mammal having a biological consequence, which may speak to the importance of codon usage in mammalian biology.

Author List

Sasine JP, Himburg HA, Termini CM, Roos M, Tran E, Zhao L, Kan J, Li M, Zhang Y, de Barros SC, Rao DS, Counter CM, Chute JP

Author

Heather A. Himburg PhD Associate Professor in the Radiation Oncology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Animals
Bone Marrow Transplantation
Cells, Cultured
Codon
Exons
Female
Hematopoiesis
Hematopoietic Stem Cells
Male
Mice
Mice, Transgenic
Models, Animal
Mutation
Primary Cell Culture
Proto-Oncogene Proteins p21(ras)
Transplantation Chimera
Whole-Body Irradiation