Research

Expression of parathyroid hormone-related protein during immortalization of human peripheral blood mononuclear cells by HTLV-1: Implications for transformation

Murali VP Nadella^1,2 , Sherry T Shu^1,2 , Wessel P Dirksen^1,2 , Nanda K Thudi¹ , Kiran S Nadella³ , Soledad A Fernandez^2,4 , Michael D Lairmore^1,2 , Patrick L Green^1,2 and Thomas J Rosol^1,2

¹  Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, USA

²  Center for Retrovirus Research, The Ohio State University, Columbus, OH, USA

³  Human Cancer Genetics, The Ohio State University, Columbus, OH, USA

⁴  Center for Biostatistics, The Ohio State University, Columbus, OH, USA

author email corresponding author email

Retrovirology 2008, 5:46doi:10.1186/1742-4690-5-46

Published:	9 June 2008

Abstract

Background

Adult T-cell leukemia/lymphoma (ATLL) is initiated by infection with human T-lymphotropic virus type-1 (HTLV-1); however, additional host factors are also required for T-cell transformation and development of ATLL. The HTLV-1 Tax protein plays an important role in the transformation of T-cells although the exact mechanisms remain unclear. Parathyroid hormone-related protein (PTHrP) plays an important role in the pathogenesis of humoral hypercalcemia of malignancy (HHM) that occurs in the majority of ATLL patients. However, PTHrP is also up-regulated in HTLV-1-carriers and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients without hypercalcemia, indicating that PTHrP is expressed before transformation of T-cells. The expression of PTHrP and the PTH/PTHrP receptor during immortalization or transformation of lymphocytes by HTLV-1 has not been investigated.

Results

We report that PTHrP was up-regulated during immortalization of lymphocytes from peripheral blood mononuclear cells by HTLV-1 infection in long-term co-culture assays. There was preferential utilization of the PTHrP-P2 promoter in the immortalized cells compared to the HTLV-1-transformed MT-2 cells. PTHrP expression did not correlate temporally with expression of HTLV-1 tax. HTLV-1 infection up-regulated the PTHrP receptor (PTH1R) in lymphocytes indicating a potential autocrine role for PTHrP. Furthermore, co-transfection of HTLV-1 expression plasmids and PTHrP P2/P3-promoter luciferase reporter plasmids demonstrated that HTLV-1 up-regulated PTHrP expression only mildly, indicating that other cellular factors and/or events are required for the very high PTHrP expression observed in ATLL cells. We also report that macrophage inflammatory protein-1α (MIP-1α), a cellular gene known to play an important role in the pathogenesis of HHM in ATLL patients, was highly expressed during early HTLV-1 infection indicating that, unlike PTHrP, its expression was enhanced due to activation of lymphocytes by HTLV-1 infection.

Conclusion

These data demonstrate that PTHrP and its receptor are up-regulated specifically during immortalization of T-lymphocytes by HTLV-1 infection and may facilitate the transformation process.