Consequences of exclusive expression in vivo of kit-ligand lacking the major proteolytic cleavage site

Abstract

Membrane growth factors that are processed to produce soluble ligands may function both as soluble factors and as membrane factors. The membrane growth factor Kitligand (KL), the ligand of the Kit receptor tyrosine kinase, is encoded at the Sl locus, and mice carrying Sl mutations have defects in hematopoiesis, gametogenesis, and melanogenesis. Two alternatively spliced KL transcripts encode two cellassociated KL protein products, KL-1 and KL-2. The KL-2 protein lacks the major proteolytic cleavage site for the generation of soluble KL, thus representing a more stable cellassociated form of KL. We investigated the consequences of exclusive expression of KL-2 in vivo. The KL gene in embryonic stem cells was modified and KL exon 6 was replaced with a PGKneoNTRtkpA cassette by homologous recombination, and mice carrying the Sl KL2 allele were obtained. Sl KL2 ͞Sl KL2 mice had only slightly reduced levels of soluble KL in their serum, suggesting that in vivo KL-2 may be processed to produce soluble KL-2S. The steady-state characteristics of the hematopoietic system and progenitor numbers were normal, and the mutant animals were not anemic. However, mast cell numbers in the skin and peritoneum were reduced and the mutant animals displayed increased sensitivity to sublethal doses of ␥-irradiation. Therefore, KL-2 may substitute for KL-1 in most situations with the exception of the production of mast cells, and induced proteolytic cleavage of KL-1 to produce soluble KL may have a role in the regeneration of hematopoietic tissue after radiation injury.

KIT/stem cell factor expression in premalignant and malignant lesions of the colon mucosa in relationship to disease progression and outcomes

“…For example, mice expressing soluble SCF but lacking transmembrane SCF have a severe phenotype affecting SCF-dependent cell lineages (46). Conversely, mice producing SCF-2 only reveal increased sensitivity to sublethal doses of Á-irradiation (47). Furthermore, transmembrane SCF is more potent than soluble SCF in maintaining the survival of multipotent hemopoietic stem cells in vitro (48).…”

Incomplete restoration of colony-stimulating factor 1 (CSF-1) function in CSF-1–deficient Csf1op/Csf1op mice by transgenic expression of cell surface CSF-1

“…[80][81][82] A juxtacrine stimulation model was proposed in which membrane-bound growth factor-mediated cell adhesion through growth factor receptor binding participates in biologic processes, such as the homing of cells to tissue locations. 83 The interaction of membrane-spanning cytokines with their receptors on adjacent cells has been shown to support cellular survival and differentiation, notably for c-kit ligand in mice [84][85][86][87] and boss in Drosophila. 88 Binding of soluble CSF-1 to the CSF-1R triggers serial molecular events, including the dimerization and autophosphorylation of CSF-1R, as well as activation of the tyrosine kinase activity of the CSF-1R and the tyrosine phosphorylation of downstream molecules.…”

Gastrointestinal stromal tumors in a mouse model by targeted mutation of the Kit receptor tyrosine kinase

“…Skin mast cell numbers were determined as described (28). Mast cells per 0.5 mm 2 skin between the epidermis and the panniculus were counted in several independent sections and averaged.…”