Expression of monocarboxylate transporter 4 in human platelets, leukocytes, and tissues assessed by antibodies raised against terminal versus pre-terminal peptides

Abstract

We compared antibodies (Abs) raised in rabbits against two non-overlapping peptides, terminal (T) and pre-terminal (PT) of the human monocarboxylate transporter (MCT4) lactate transporter in a variety of human tissues. Upon stringent SDS extraction, the PT Ab recognized a major 32 kDa band in many tissues, but not in leukocytes, while the T Ab recognized a 45 kDa band in leukocytes but only in a few other tissues. In two cell lines, human adult retinal pigment epithelial and Madin-Darby canine kidney, however, both Abs identiWed the same 45 kDa band only, whether extracted by stringent SDS or by a mild Triton X-100 procedure. Applying Triton X-100 and milder SDS methods to human tissues led us to conclude that: (1) MCT4 is more labile to proteolysis than MCT1 or 2; (2) the proteolysis involves an enzyme system which is absent from the cell lines, is of variable content in human tissues, and is accelerated by SDS and/or heat; (3) a major product is the 32 kDa band, which is missing the C-terminal peptide, since it is seen by the Ab to MCT4-PT, but not the Ab to MCT4-T; (4) this truncated 32 kDa form is prone to aggregate, producing oligomers also detected only by the MCT4-PT; (5) the 32 kDa form may have a physiological function, since (except in the cell lines and monocytes) it is the major form seen with the PT Ab even with our mildest extractions, and since MCT4-PT stained two compartments that were not stained by the T Ab in our immunohistochemistry survey: the capsule of the muscle spindle, and the cytoplasm of the lymphocyte; (6) platelets contained MCT4, stained by both Abs, and veriWed by the 45 kDa band on Western blotting, in addition to the presence of MCT2 that we had demonstrated previously [N. Merezhinskaya, S.A. Ogunwuyi, F.G. Mullick, W.N. Fishbein, Presence and localization of three lactic acid transporters (MCT1, -2, and -4) in separated human granulocytes, lymphocytes, and monocytes, J.

Expression, cellular localization, and functional role of monocarboxylate transporter 4 (MCT4) in the gastrointestinal tract of ruminants

“…1A). This band is consistent with the molecular mass reported earlier for MCT4 in human skeletal muscle (43-kD; Thomas et al, 2005) and human platelets and leukocytes (45-kD; Merezhinskaya et al, 2004Merezhinskaya et al, , 2006, as well as with the 47-kD in reindeer rumen and small intestine (Koho et al, 2005). The considerable regional differences observed in the protein level of MCT4 among the different segments of the bovine gastrointestinal tract, as indicated by the densitometric analysis (Fig.…”

Monocarboxylate transporters in the brain and in cancer

“…MCT4 was shown to be expressed by a subset of muscle cells composing glycolytic (type II) fibers [49] , [50] , [96] . It is also present in some types of white blood cells, including macrophages [66] , [97] , [98] . In the central nervous system, the transporter is found exclusively in astrocytes [83] , [99] , with the exception of tanycytes in the hypothalamus [86] .…”

The Human Carbonic Anhydrase II in Platelets: An Underestimated Field of Its Activity

“… A potential role of carbonic anhydrase II (CAII) in regulating ASA response [ 30 – 32 , 37 ]. GLUT3: glucose transporter; MCT4: H+/monocarboxylate transporter; AE: anion exchanger; NHE1: the Na+/H+ exchanger; COX-1: cyclooxygenase-1; TxA 2 : thromboxane A 2 .…”