Login to Access Video or Poster Abstract: MP83-11
Sources of Funding: none

Introduction

Leucine stimulates cancer cell proliferation through the mTOR pathway, therefore, inhibiting leucine transporters can be a novel therapeutic strategy. One of leucine transporters, L-type amino acid transporter (LAT) 1 (SLC7A5), a Na⁺-independent amino acid transporter, has been reported to be selectively expressed in many cancer cells. Recently it has been shown that primary prostate cancer expresses LAT3 (SLC43A1), while castration resistant or highly aggressive prostate cancer expresses LAT1 as a main leucine transporter. In this study, we examine leucine transporters during acquisition of hormone independence.

Methods

A new &[Prime]LN-abl&[Prime] cell line was established after culturing LNCaP cells for 6 months under androgen-free conditions, which is a model of castration resistant prostate cancer (CRPC) with androgen receptor expression. Uptake of ¹⁴C leucine was examined in the presence or absence of LAT inhibitors or Na⁺. Expression of a major leucine transporter was inhibited by siRNA in LN-abl cells. In silico analysis of leucine transporter expression was examined using Oncomine for different progression status of prostate cancers in clinical data sets.

Results

Cell viability was decreased to 10% in the absence of leucine. LNCaP cells principally expressed LAT3, and their leucine uptake was more than 90% Na⁺-independent. In LN-abl cells, Na⁺-dependent uptake of leucine was 3.8 pmol/mgprotein/min, while, Na⁺-independent uptake was only 0.52, therefore, leucine uptake of LN-abl was largely (~85%) Na⁺-dependent. y⁺LAT2 (SLC7A6) expression was confirmed in LN-abl, however, expression of LAT1, LAT3, y⁺LAT1 (SLC7A7), ATB0⁺ (SLC6A14), B0AT1 (SLC6A19), B0AT2 (SLC6A15) or b0⁺AT (SLC7A9) were not observed. Knockdown of y⁺LAT2 lead to significant leucine uptake inhibition (40%) and cell growth inhibition (20%) in LN-abl cells. In silico analysis revealed that more frequent up-regulation of SLC7A6 (y⁺LAT2) was observed in hormone resistant or metastatic samples in 2 data sets. In addition, some advanced prostate cancer appeared to express high levels of LAT3, suggesting heterogeneity in leucine transporter expression among different prostate cancers.

Conclusions

New CRPC cell line with increased expression of y⁺LAT2 was established in vitro. This is consistent with the fact that at least some advanced stage prostate cancers express y⁺LAT2 in Oncomine data. Considering the diversity of leucine transporter expression, target of anti-leucine transporter therapy should be individualized.

Funding

none