Comparative expression profile of orphan receptor tyrosine kinase ROR1 in Iranian patients with lymphoid and myeloid leukemias

Abstract

It has recently been shown that ROR1, a member of the receptor tyrosine kinase family, is overexpressed in leukemic B cells of Chronic Lymphocytic Leukemia (CLL) and a subset of Acute Lymphoblastic Leukemia (ALL). In this comparative study the expression profile of ROR1 mRNA was investigated in Iranian patients with CLL and Acute Myelogenous Leukemia (AML) and the results were compared with those previously reported in our Iranian ALL patients. RT-PCR was performed on bone marrow and/or peripheral blood samples of 84 CLL and 12 AML patients. CLL samples were classified into immunoglobulin heavy chain variable region (IGHV) gene mutated (n = 55) and unmutated (n = 29) and also indolent (n = 42) and progressive (n = 39) subtypes. ROR1 expression was identified in 94% of our CLL patients, but none of the AML patients expressed ROR1. No significant differences were observed between different CLL subtypes for ROR1 expression. Taken together the present data and our previous results on ROR1 expression in ALL, our findings propose ROR1 as a tumor-associated antigen overexpressed in a large proportion of lymphoid (CLL and ALL), but not myeloid (AML) leukemias. Expression of ROR1 seems to be associated to lineage and differentiation stages of leukemic cells with a potential implication for immunotherapy.

Keywords: Acute myelogenous leukemia; Chronic lymphocytic leukemia; ROR1; RT-PCR.

Figure 1

Representative expression profile of ROR1 mRNA in peripheral blood (PB) or bone marrow (BM) samples of a number of patients and healthy subjects. PCR amplicons of ROR1 (545 bp) and β-actin (321 bp) genes were electrophoresed on 1.5% ethidium bromide- stained gel and photographed. Lane 1: size marker; Lanes 2-5: CLL (PB); Lanes 6-9: AML (6 and 8: PB and 7 and 9: BM); Lanes 10-12: healthy subjects (PB)

Figure 2

Relative expression levels of ROR1 mRNA in CLL, ALL and AML patients and normal subjects. The horizontal line denotes the cutoff value obtained from the normal samples; the data of ALL patients has been taken from ref 17. Relative expression of ROR1 mRNA levels in samples was determined by calculation of the ratio of ROR1 PCR product band density to that of β-actin. Baseline level of ROR1 expression was assigned as mean + 1SD of ROR1/ β-actin ratio of normal subjects. *** : p-values of less than 0.0001 ** : p-values of less than 0.005

Figure 3

Representative expression profile of ROR1 in different subgroups of CLL patients. PCR amplicons of ROR1 (545 bp) and β-actin (321 bp) genes were electro-phoresed on 1.5% ethidium bromide-stained agarose gel and photographed. Lanes 1-4: patients with indolent disease; Lanes 5-7: patients with progressive disease; lane 8: size marker; Lanes 9-11: patients with mutated leukemic cells; Lanes 12-14: patients with unmutated leukemic cells