Mutant p53 in bone marrow stromal cells increases VEGF expression and supports leukemia cell growth.
OBJECTIVE
Genetic alterations, including p53 mutations, have been identified in the stroma of solid tumors and are thought be involved in the induction of tumor growth and metastasis. We tested the hypothesis that somatic molecular alterations in bone marrow stromal cells provide a favorable growth environment for leukemic cells.


METHODS
We established an in vitro model consisting of stroma expressing mutant p53 (Cys135Ser) to study its ability to support growth of cells from a pre-B acute lymphoblastic leukemia (ALL) cell line. Normal and leukemic bone marrow stromal cells were screened for p53 mutations by mutant-specific ELISA, SSCP, and direct sequencing. Secretion of vascular endothelial growth factor (VEGF) was measured by quantitative ELISA.


RESULTS
Transfection of stromal cells with mutant p53 increased synthesis of VEGF and supported the growth of leukemic cells. An ELISA-based assay suggested the occurrence of in vivo p53 alterations in bone marrow stromal cells from 2 of 12 ALL patients screened. Direct sequencing of one of these samples revealed a somatic heterozygous p53 gene mutation (Asp49His). This sample secreted more VEGF and provided increased growth support to leukemic cells. The ability of Asp 49His-p53 to increase the expression of VEGF was confirmed with transfection experiments in a p53-null cell line.


CONCLUSIONS
Our findings indicate that genetic alterations, such as p53 mutations, in stromal cells can increase stromal-derived support of leukemia growth. Increased synthesis of pro-angiogenic cytokines, such as VEGF, may constitute one possible pathway by which this process is mediated.
Narendran
Aru
A
Southern Alberta Children's Cancer Program, Alberta Children's Hospital, Calgary, Alberta, Canada.
Ganjavi
Hooman
H
Morson
Natalie
N
Connor
Alison
A
Barlow
Jason W
JW
Keystone
Edward
E
Malkin
David
D
Freedman
Melvin H
MH
D019943:Amino Acid Substitution; D002455:Cell Division; D002648:Child; D018920:Coculture Techniques; D016228:Endothelial Growth Factors / Q000096:biosynthesis* / Q000235:genetics; D015973:Gene Expression Regulation, Leukemic; D016158:Genes, p53; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D008222:Lymphokines / Q000096:biosynthesis* / Q000235:genetics; D020125:Mutation, Missense; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D015452:Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000473:pathology*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000473:pathology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D017154:Stromal Cells / Q000166:cytology / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000473:pathology; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D009363:Neoplasm Proteins; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors