Enhanced tumorigenicity caused by truncation of the extracellular domain of GP125/CD98 heavy chain

Abstract

GP125/CD98 is a heterodimeric 125-kDa glycoprotein, which consists of an 85-kDa heavy chain (hc) and a 40-kDa light chain (lc), and is strongly expressed on the cell surface of various tumor cells, irrespective of their tissue of origin. We have recently demonstrated that overexpression of the CD98hc cDNA causes malignant transformation of NIH3T3 cells. To investigate the function of the extracellular domain of CD98hc in cell proliferation and malignant transformation, we established two NIH3T3-derived clones transfected with human truncated CD98hc cDNAs, and compared their characteristics with parental NIH3T3 and clones transfected with full-length CD98hc cDNA. Truncated as well as full-length CD98hc-transfected clones grew to a higher saturation density than control cells. E ciency of colony formation in soft agar was augmented in all CD98hc-transfected clones, and the degrees of augmented colony formation of the transfectants expressing fulllength CD98hc of 529 a.a. or truncated CD98hc of 418 a.a. were reduced by anti-human CD98hc antibodies, while that of the transfectant expressing truncated CD98hc of 237 a.a. lacking the epitopes recognized by anti-human CD98hc antibodies was not a ected by the addition of antibodies. CD98hc-transfected clones developed tumors in athymic mice, and tumor growth of truncated CD98hc-transfected clones was faster than that of full-length CD98hc-transfected clones. Oncogene (2000) 19, 6209 ± 6215.

Adenoviral modulation of the tumor‐associated system L amino acid transporter, LAT1, alters amino acid transport, cell growth and 4F2/CD98 expressionwith cell‐type specific effects in cultured hepatic cells

“…It has been shown previously that 4F2 overexpression in NIH 3T3 cells results in changes consistent with malignant transformation 17,20 and monoclonal antibodies against 4F2 have been shown to inhibit tumor cell nucleic acid synthesis and proliferation of several cell types. 21,22 The malignant alterations, however, required association with the CD98 complex light chain.…”

“…[8][9][10][11][12][13] The glycoprotein-associated transporters are a novel class of amino acid transporters recently the subject of much interest not only in relation to transport but also to CD98-linked functions in cell activation, integrin signaling, cell fusion and malignant transformation. [14][15][16][17] Our research has utilized a tetracycline-inducible adenoviral expression system (TET-Off) system to alter levels of LAT1 and 4F2 in vitro. We have increased LAT1 expression in normal hepatic cells to determine functional changes occurring in processes associated with cancer.…”

NIH3T3 cells overexpressing CD98 heavy chain resist early G1 arrest and apoptosis induced by serum starvation

“…Stable NIH3T3 transfectant clones expressing full-length human CD98hc protein (NIH/hH-1, NIH/hH-2 and NIH/hH-3) and a control NIH3T3 transfectant clone (NIH/neo) were maintained in DMEM containing 10% FBS and 400 lg/mL of Geneticin disulfate (G418; Wako Pure Chemical Industries, Osaka, Japan). (31,33) Multiple aliquots of individual clones (passages 5-10) were frozen, and each aliquot was used for no more than 2 weeks, to avoid potential phenotypic changes. Expression of human CD98hc protein on the cell surface of each clone was confirmed periodically by flow cytometry, as described previously.…”

“…Several groups report the higher expression of CD98 in restricted normal tissues, which contain actively dividing cells. (1,2,(21)(22)(23)(24)(25) As to the involvement of CD98 in cancers, we have reported higher expression of CD98 in various cancer cells using specific anti-CD98hc mAb, (2,26) growth inhibition of cancer cells by anti-CD98hc mAb (27)(28)(29) or by liposomes containing anticancer drug and coated with anti-CD98hc mAb, (30) malignant transformation of mouse fibroblasts by DNA transfection of human and rat cDNA of CD98hc, (31)(32)(33) and cooperation between CD98hc and CD98lc in the malignant transformation. (32) We have recently demonstrated that the CD98lc responsible for CD98hc-mediated malignant transformation is L-type amino-acid transporter 1 (LAT1), also referred to as solute carrier (SLC) 7A5, among six CD98lc, namely, LAT1, LAT2 (SLC7A8), y+LAT1 (SLC7A7), y+LAT2 (SLC7A6), asc1 (SLC7A10) and xCT (SLC7A11), from experimental genetics using LAT1 gene-disrupted chicken DT40 cells.…”

“…As mentioned above, we have found that murine fibroblasts transfected with human or rat CD98hc cDNA show various malignant phenotypes. (31)(32)(33) Proliferation of normal mammalian cells is directly related to the cell cycle, (35) and deregulation of cell cycle progression results in oncogenesis. (36) To understand the function of CD98 with respect to cellular proliferation and malignancy, in the present study, we analyze the cell-cycle progression and expression of G1 cyclins, CDK, and their inhibitors using NIH3T3 clones transfected with full-length cDNA of human CD98hc.…”