Parathyroid hormone-related protein (PTHrP), an oncoprotein expressed in 50-75% of human lung carcinomas, is a multifunctional molecule that undergoes post-translational processing. Processing has significant implications for patient outcome. From our previous work, we know that tumor expression of carboxyl-terminal PTHrP by itself is a positive prognostic indicator in women with non-small cell lung carcinoma (NSCLC), while processing to solely amino-terminal PTHrP is associated with shorter patient survival. Interestingly, lung carcinomas in females are likely to express carboxyl PTHrP alone and only female patients demonstrate a survival benefit from when expressing this domain. In contrast, carcinomas in males usually contain both PTHrP epitopes and do not show a survival benefit. Thus, a sex-based difference in relative expression of amino and carboxyl-terminal PTHrP contributes to a sex-dependent difference in outcome. Preliminary data from a mouse lung cancer model suggest that testosterone controls the sex difference in amino and carboxyl PTHrP. As a hypothesis, we propose that the relative expression of amino- and carboxyl-terminal PTHrP is a function of processing that varies between male and female carcinomas because of sex steroids. Furthermore, amino and carboxyl PTHrP regulate tumor progression directly through stimulatory and inhibitory effects, respectively, on lung cancer cell growth, survival and invasiveness.
Aim 1 will establish the effects of androgens on processing of PTHrP in lung carcinoma in over 14 different lung cancer cell lines, in orthotopic lung carcinomas in syngeneic or immunocompromised mice, and in fresh human lung carcinomas. The studies will consider interactions with histology, sex, smoking history, mutational status in common, important molecular drivers and other covariates. Processing will be assessed by region-specific immunoassay, in vitro PTHrP proteolysis assays and mass spectrometry.
Aim 2 will define the regulatory effects of PTHrP processing on lung carcinoma progression in the mouse models. Experiments will study PTHrP forms that have been processed by gene truncation to lack amino or carboxyl PTHrP domains. Additional experiments will study PTHrP mutants resistant to key processing steps.
Aim 3 will identify proteases that regulate androgen-dependent PTHrP processing and the associated effects on tumor progression. The experiments will use activity-based probes to isolate and sequence proteases regulated by androgens. Subsequent experiments will confirm the role of these proteases in PTHrP processing. The translational benefit of this project will result from learning how hormonal pathways affect the balance between amino PTHrP and carboxyl PTHrP in lung cancer and identifying the proteases mediating those effects. Novel, improved treatments could be sought in drugs that targeted the androgen regulatory pathway or the proteases to augment carboxyl PTHrP relative to amino PTHrP and prolong survival. This goal may be close to fruition because we have found individual cyclic guanidine compounds , a class of molecule with known effects on serine protease activity, that reduce amino PTHrP in lung cancer.
Lung carcinoma is a common form of cancer in veterans due to the high prevalence of smoking. Managing lung cancer consumes considerable time and resources, unfortunately too often with minimal benefit to the patients we serve. This project will investigate sex-dependent aspects of lung cancer, an important feature since the disease afflicts both sexes and the ranks of women veterans are expanding progressively. This project may lead to advances in caring for patients with lung cancer. It will evaluate pathways by which PTHrP might regulate growth of lung cancer carcinomas. This project may identify new markers related to PTHrP that could be used to identify lung cancers, assess tumor grade or malignant potential, or assist prognosis. As a long-term objective, the projective may lay the groundwork for development of PTHrP-based therapeutic interventions for lung cancer.