Heme in intestinal epithelial cell turnover, differentiation, detoxification, inflammation, carcinogenesis, absorption and motility

Table 1 Proteins involved in intestinal heme-iron absorption along with their function, location and whether they are regulated by iron

Protein	Function	Location	Regulation by Fe
Heme receptor	Receptor for heme	?	Inversely
HCP1	Transporter of heme	AM -> BC	Constant
FLVCR	Heme exporter	?	Unknown
Ferritin	Iron storage	C	Directly
DMT1	Fe(II) importer	AM+Lys	Inversely
Ferroportin	Fe(II) exporter	BL AM	Inversely
Hephaestin	Ferroxidase + ?	SN, BL	Constant
HO 1	Degradation of heme	C	Inversely
HO 2	Degradation of heme	SMC, EN	Constant
HFE	Regulator	TW	Inversely
TfR1	Tf:Fe endocytosis	BL, SN	Constant
Transferrin	Endosomal iron transport	C	Inverse

DMT1 = divalent metal transporter 1; HO = heme oxygenase; HCP1 = heme carrier protein 1; FLVCR = Feline leukaemia virus, subgroup C receptor; HFE = hemochromatosis protein; TfR1 = transferrin receptor 1; AM = apical membrane; BL = basolateral membrane; SN = supranuclear; LM = lateral membrane; Lys = Lysosomes; TW = terminal web; C = cytoplasm; BC = basal cytoplasm; SMC = smooth muscle cells, EN = enteric nerves; ? = putative; Tf:Fe = transferrin iron.