In certain aspects, the invention provides isolated SLC5A8 (also referred to as Hui1) nucleic acid molecules, which encode novel sodium solute symporter members. The invention also provides antisense nucleic acid molecules, recombinant expression vectors containing SLC5A8 nucleic acid molecules, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a SLC5A8 gene has been introduced or disrupted. The invention still further provides isolated SLC5A8 proteins, fusion proteins, antigenic peptides, and anti-SLC5A8 antibodies. Diagnostic methods utilizing compositions of the invention are also provided. In other aspects, the invention provides methods and compositions for detecting and treating SLC5A8-associated cancer. Differential methylation of the SLC5A8 nucleotide sequences has been observed in SLC5A8-associated cancer, such as colon cancer, breast cancer, thyroid cancer, or stomach cancer.