The protein tyrosine kinase receptors, designated Rse and HPTK6, have been purified from human and/or murine cell tissues. Rse and HPTK6 have been cloned from a cDNA library of a human liver carcinoma cell line (i.e., Hep 3B) using PCR amplification. Provided herein are nucleic acid sequences encoding Rse and HPTK6 useful as diagnostics and in the recombinant preparation of Rse and HPTK6. Rse and HPTK6 are used in the preparation and purification of antibodies thereto and in diagnostic assays.