Variant Transcript of ROR1 ENST00000545203 Does Not Encode ROR1 Protein.

Drs. John and Ford reported in biomedicines that a variant transcript encoding receptor tyrosine kinase-like orphan receptor 1 (ROR1), namely ENST00000545203 or variant 3 ( ROR1 ^V3 ), was a predominant ROR1 transcript of neoplastic or normal cells in the Bioinformatic database, including GTEx and the 33 datasets from TCGA. Unlike the full-length ROR1 transcript, Drs. John and Ford deduced that ROR1 ^V3 encoded a cytoplasmic ROR1 protein lacking an apparent signal peptide necessary for transport to the cell surface, which they presumed made it unlikely to function as a surface receptor for Wingless/Integrated (Wnt) factors. Moreover, they speculated that studies evaluating ROR1 via immunohistochemistry using any one of several anti-ROR1 mAbs actually may have detected cytoplasmic protein encoded by ROR1 ^V3 and that anti-cancer therapies targeting surface ROR1 thus would be ineffective against "cytoplasmic ROR1-positive" cancers that express predominately ROR1 ^V3 . We generated lentivirus vectors driving the expression of full-length ROR1 or the ROR1 ^v3 upstream of an internal ribosome entry site (IRES) of the gene encoding a red fluorescent reporter protein. Although we find that cells that express ROR1 have surface and cytoplasmic ROR1 protein, cells that express ROR1 ^v3 neither have surface nor cytoplasmic ROR1, which is consistent with our finding that ROR1 ^v3 lacks an in-frame initiation codon for ribosomal translation into protein. We conclude that the detection of ROR1 protein in various cancers cannot be ascribed to the expression of ROR1 ^v3 .