We identified the 6 human paralogous COBW domain-containing (CBDW) genes as potentially responsive to zinc through an in silico search for an element (ZRE; Zinc Responsive Element) found to mediate transcriptional repression of the zinc transporter SLC30A5 gene in Caco-2 cells in response to zinc. The function of the CBDW proteins is unknown. Our hypothesis was that CBWD genes respond to zinc in Caco-2 cells and that CBDW protein expression is affected by zinc. All data are stated as mean ± S.E.M in arbitrary units and statistical analysis was by Student’s unpaired t-test. The abundance of the CBWD transcript in Caco-2 cells, normalised to GAPDH, was measured by RT-qPCR to be ~50% lower (P<0.001) in cells treated for 24 h with 100 μM zinc (0.48 ± 0.06, n=6) compared with 3 μM zinc (1.00 ± 0.09, n=6). Zinc-regulated CBDW transcription and the role of the ZRE was investigated using plasmid constructs comprising the region -1078 to +98 of the CBDW3 gene, relative to the start of transcription, upstream of the β-galactosidase reporter gene in the vector pBlueTOPO (Invitrogen). Reporter gene expression was lower (P<0.001) at 100 μM zinc (0.73 ± 0.04, n=23) compared with 3 μM zinc (1.00 ± 0.04; n=24) in transfected Caco-2 cells treated with zinc for 24 h. The response of the reporter gene to zinc was attenuated (P<0.01) by mutating the ZRE to a random sequence (1.00 ± 0.03 at 3 µM zinc; 0.90 ± 0.02 at 100 µM zinc; n=12), consistent with the ZRE having a role in mediating the transcriptional response to zinc. Human CBWD3 protein, incorporating a C-terminal FLAG tag, was expressed transiently from a plasmid construct comprising the full ORF of the human CBDW3 gene in the vector pCMV6Entry (Origene) in CHO cells treated for 24 h with 3 or 100 μM zinc. Western blot analysis using an anti-FLAG antibody indicated greater abundance (P<0.05) of the recombinant protein resolved by SDS-PAGE at the expected molecular weight (~44 kDa) in cells cultured at the higher zinc concentration (1.00 ± 0.12 at 3 µM zinc; 2.57 ± 0.36 at 100 µM zinc; derived by densitometric quantification of band intensity, n=3-4). Preliminary observations indicated increased abundance at the lower zinc concentration of an anti-FLAG immunoreactive band of a lower molecular weight (~30 kDa), possibly indicative of zinc-dependent cleavage. These observed effects of zinc availability on the expression of the CBDW genes and CBDW protein are consistent with the view that the human CBDW proteins play a role in zinc homeostasis in intestinal epithelial cells. Further studies, including the identification of CBDW protein binding partners, description of tissue and sub-cellular distribution, and effects of zinc and other divalent metals on these measures, may help to elucidate this role.