Smith A, Eskew J D, Borza C M, Pendrak M, Hunt R C
Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City 64110-2499, USA.
Exp Cell Res. 1997 May 1;232(2):246-54. doi: 10.1006/excr.1997.3526.
Heme-hemopexin supports and stimulates proliferation of human acute T-lymphoblastic (MOLT-3) cells, suggesting the participation of heme in cell growth and division. MOLT-3 cells express approximately 58,000 hemopexin receptors per cell (apparent Kd 20 nM), of which about 20% are on the cell surface. Binding is dose- and temperature-dependent, and growth in serum-free IMDM medium is stimulated by 100-1000 nM heme-hemopexin, consistent with the high affinity of the receptor for hemopexin, and maximal growth is seen in response to 500 nM complex. Growth was similar in defined minimal medium supplemented with either low concentrations of heme-hemopexin or iron-transferrin, and either of these complexes were about 80% as effective as a serum supplement. Heme-hemopexin, but not apo-hemopexin, reversed the growth inhibition caused by desferrioxamine showing that heme-iron derived from heme catabolism is used for cell growth. Cobalt-protoporphyrin (CoPP)-hemopexin, which binds to the receptor but is not transported intracellularly [Smith et al., (1993) J. Biol. Chem. 268, 7365], also stimulated cell proliferation in serum-free IMDM but did not "rescue" the cells from desferrioxamine. Furthermore, CoPP-hemopexin effectively competed for the hemopexin receptor with heme-hemopexin and diminished its growth stimulatory effects. In addition, protein kinase C (PKC) is translocated to the plasma membrane within 5 min after heme-hemopexin is added to the medium, reaches maximum activity within 5-10 min, and declines to unstimulated levels by 30 min. Heme-hemopexin and CoPP-hemopexin both augmented MOLT-3 cell growth stimulated by serum. Thus, heme-hemopexin not only functions as an iron source for T-cells but occupancy of the hemopexin receptor itself triggers signaling pathway(s) involved in the regulation of cell growth. The stimulation of growth of human T-lymphocytes by heme-hemopexin is likely to be a physiologically relevant mechanism at sites of injury, infection, and inflammation.
血红素 - 血红素结合蛋白支持并刺激人急性T淋巴细胞（MOLT - 3）细胞的增殖，这表明血红素参与细胞生长和分裂。MOLT - 3细胞每个细胞表达约58,000个血红素结合蛋白受体（表观解离常数Kd为20 nM），其中约20%位于细胞表面。结合具有剂量和温度依赖性，在无血清IMDM培养基中，100 - 1000 nM的血红素 - 血红素结合蛋白可刺激细胞生长，这与受体对血红素结合蛋白的高亲和力一致，500 nM复合物可观察到最大生长反应。在添加低浓度血红素 - 血红素结合蛋白或铁转铁蛋白的限定基础培养基中生长情况相似，这两种复合物的效果约为血清补充剂的80%。血红素 - 血红素结合蛋白而非脱辅基血红素结合蛋白可逆转去铁胺引起的生长抑制，表明血红素分解代谢产生的血红素铁用于细胞生长。钴原卟啉（CoPP） - 血红素结合蛋白可与受体结合但不被转运到细胞内[史密斯等人，（1993年）《生物化学杂志》268, 7365]，在无血清IMDM中也刺激细胞增殖，但不能使细胞从去铁胺的抑制中“恢复”。此外，CoPP - 血红素结合蛋白可与血红素 - 血红素结合蛋白有效竞争血红素结合蛋白受体并减弱其生长刺激作用。另外，在向培养基中添加血红素 - 血红素结合蛋白后5分钟内，蛋白激酶C（PKC）转位至质膜，在5 - 10分钟内达到最大活性，并在30分钟时降至未刺激水平。血红素 - 血红素结合蛋白和CoPP - 血红素结合蛋白均增强血清刺激的MOLT - 3细胞生长。因此，血红素 - 血红素结合蛋白不仅作为T细胞的铁源发挥作用，而且血红素结合蛋白受体的占据本身会触发参与细胞生长调节的信号通路。血红素 - 血红素结合蛋白对人T淋巴细胞生长的刺激可能是损伤、感染和炎症部位的一种生理相关机制。
