The reduced folate carrier (RFC) is a major folate transport system in mammalian 
cells. RFC is highly expressed in the intestine and believed to play a role in 
folate absorption. Studies from our laboratory and others have characterized 
different aspects of the intestinal folate absorption process, but little is 
known about possible existence of accessory protein(s) that interacts with RFC 
and influences its physiology and/or cell biology. We investigated this issue by 
employing a bacterial two-hybrid system to screen a BacterioMatch II human 
intestinal cDNA library using the large intracellular loop between transmembrane 
domains 6 and 7 of the human RFC (hRFC) as bait. Our screening has resulted in 
the identification of dynein light chain road block-1 (DYNLRB1) as an 
interacting partner with hRFC. Existence of a direct protein-protein interaction 
between hRFC and DYNLRB1 was confirmed by in vitro pull-down assay and in vivo 
mammalian two-hybrid luciferase assay and coimmunoprecipitation analysis. 
Furthermore, confocal imaging of live human intestinal epithelial HuTu-80 cells 
demonstrated colocalization of DYNLRB1 with hRFC. Coexpression of DYNLRB1 with 
hRFC led to a significant (P < 0.05) increase in folate uptake. On the other 
hand, inhibiting the endogenous DYNLRB1 with gene-specific small interfering RNA 
or pharmacologically with a specific inhibitor (vanadate) led to a significant 
(P < 0.05) decrease in folate uptake. This study demonstrates for the first time 
the identification of DYNLRB1 as an interacting protein partner with hRFC. 
Furthermore, DYNLRB1 appears to influence the function and cell biology of hRFC.