PTBP1 and lung adenocarcinoma: However, our previous studies using a metastatic cell model derived from lung adenocarcinoma have shown that (i) PTB can down-regulate the expression of hypoxia-inducible factor 1α which is a critical factor helping tumor cells cope with harsh microenvironment resulted from vigorous proliferation of tumor cells, (ii) PTB expression is down-regulated in cells possessing higher metastatic capability, and (iii) PTB is able to inhibit cell invasion [10].