A subset of bone marrow stromal cells regulate ATP-binding cassette gene expression via insulin-like growth factor-I in a leukemia cell line.

The importance of the insulin-like growth factor, IGF, as a signaling axis in cancer development, progression and metastasis is highlighted by its effects on cancer cells, notably proliferation and acquired resistance. The role of the microenvironment within which cancer cells evolve and which mediates this effect is far from clear. Here, the involvement of IGF-I in inducing multidrug resistance in a myeloid leukemia cell line, grown in the presence of bone marrow-derived stromal cells called 'Hospicells' (BMH), is demonstrated. We found that i) drug sensitive as well as resistant leukemia cells express IGF-I and its receptor IGF-IR. However, the resistant cells were found to secrete high levels of IGF-I. ii) Presence of exogenous IGF-I promoted cell proliferation, which decreased when an inhibitor of IGF-IR (picropodophyllin, PPP) was added. iii) BMH and IGF-I are both involved in the regulation of genes of the ATP binding cassette (ABC) related to resistance development (MDR1, MRP1, MRP2, MRP3 and BCRP). iv) The levels of ABC gene expression by leukemia cells were found to increase in the presence of increasing numbers of BMH. However, these levels decreased when IGF-IR was inhibited by addition of PPP. v) Co-culture of the drug-sensitive leukemia cells with BMH induced protection against the action of daunorubicin. This chemoresistance was amplified by the presence of IGF-I whereas it decreased when IGF-IR was inhibited. Our results underline the role of microenvironment in concert with the IGF-1 pathway in conferring drug resistance to leukemia cells.

Vascular endothelial growth factor receptor-1 (VEGFR-1) expression in human corneal fibroblast decreased with age.

PURPOSE: Mechanisms by which fibroblast networks between stromal lamellae are laid in the corneal stroma are far from clear. We have investigated the role of vascular endothelial growth factor receptors (VEGFRs) by in vitro studies in the human corneal network formation obtained from donors whose ages ranged from 19 to 89 years. METHODS: Corneal fibroblasts were prepared from cornea donations. The functional properties of these cells to form networks were analyzed using a semi solid matrix (substratum) of Matrigel. The presence of VEGF receptor-1 (VEGFR-1) and the functionality in these fibroblasts were investigated using immunofluorescence, molecular analysis (gene microarray, reverse transcription polymerase chain reaction [RT-PCR] and VEGFR siRNA transfections), and cell culture. RESULTS: Corneal fibroblasts from 61 donors were classified into two groups according to whether they formed (82%) a reticulum on Matrigel or not (18%). By RT-PCR and immunofluorescence analysis, we showed that corneal fibroblasts expressed VEGFR-1 (mRNA and protein). Further, cell culture analysis revealed that only the network (reticulum) forming corneal fibroblast expressed VEGFR-1 in contrast to non network-forming fibroblasts. Use of inhibitors such as VEGFR-1 siRNA transfection or neutralizing antibody (Avastin) indicated that VEGFR-1 was essential to the formation of the corneal network in vitro. CONCLUSIONS: The cell reticulum formation seemed to be directly related to the expression of VEGFR-1 in the corneal fibroblast, and this expression decreased with age. The decrease in VEGFR-1 expression is probably related to the diminution of autocrine functions, which may alter the overall tissular homeostasis. This may culminate in the gradual development of poor vision, which is observed in certain pathologies and in aging individuals.