Carcinoma of the lung and cigarette smoking. Effect on serum ribonuclease activity

Emerging biological functions of ribonuclease 1 and angiogenin

Pancreatic-type ribonucleases (ptRNases) are a large family of vertebrate-specific secretory endoribonucleases. These enzymes catalyze the degradation of many RNA substrates and thereby mediate a variety of biological functions. Though the homology of ptRNases has informed biochemical characterization and evolutionary analyses, the understanding of their biological roles is incomplete. Here, we review the functions of two ptRNases: RNase 1 and angiogenin. RNase 1, which is an abundant ptRNase with high catalytic activity, has newly discovered roles in inflammation and blood coagulation. Angiogenin, which promotes neovascularization, is now known to play roles in the progression of cancer and amyotrophic lateral sclerosis, as well as in the cellular stress response. Ongoing work is illuminating the biology of these and other ptRNases.

The association of elevated 2',5'-oligoadenylate-dependent RNase L with lung cancer correlated with deficient enzymatic activity and decreased capacity of RNase L dimerization

RNase L mediates critical cellular functions including antiviral, proapoptotic, antiproliferative and tumor suppressive activities. In this study, the expression and function of RNase L in lung cancer cells were examined. Interestingly we have found that the expression of RNase L in lung cancer cells was 3- and 9-fold higher in its mRNA and protein levels, but a significant decrease of its enzymatic activity when compared to that in corresponding normal lung cells. Further investigation revealed that 2-5A-induced dimerization of the RNase L protein, a necessary prerequisite for activation of RNase L, was inhibited, as a result of that RLI, a specific inhibitor of RNase L, was remarkably up-regulated in the cancer cells. Our findings provide new insight into how cancer cells escape normal growth-regulating mechanisms to form a tumor and the information may be useful for the design of novel strategies for treating lung cancer through regulating RNase L activity.

Influence of nutritional status on circulatory ribonuclease C levels in patients with cancer

The influence of a variety of clinical and biochemical parameters on the activities in serum of ribonuclease (RNAse) selective for polycytidylic acid (RNAse C) were examined in 90 adult patients with cancer. The clinical data base determined on each patient included: RNAse C level, carcinoembryonic antigen (CEA) level, age, sex, race, presence (or absence of metastases, type of cancer, site of metastasis, renal function blood urea nitrogen [BUN], creatinine), hepatic function (bilirubin, alkaline phosphatase), and nutritional status (percent ideal body weight, percent weight loss, and albumin). Common tumor types studied included: colon (21), lung (18), breast (15), and hepatocellular carcinoma (10). For comparison, 175 nonmalignant control patients were studied to establish the normal range for RNAse. In patients with cancer, RNAse levels were increased in 57% and CEA levels were above 10 ng/dl in 36%. Although patients with BUN greater than 25 mg/dl or creatinine greater than 1.5 mg/dl were not entered on the study, nonetheless, RNAse was significantly (P less than 0.05) associated with both BUN and creatinine. Nutritional status also had an important influence on RNAse levels as both percent weight loss and percent ideal body weight were significantly (P less than 0.05) associated with circulatory RNAse: weight loss resulted in higher RNAse levels. These results account in part for the increased RNAse levels seen in those malignant conditions such as pancreatic and lung cancer commonly associated with weight loss in advanced stage. The possibility that circulatory RNAse C determination will provide a sensitive means for assessing nutritional status in cancer patients will require prospective evaluation.

Alteration of human serum ribonuclease activity in malignancy

A review of the literature and current biochemical studies is presented which provides significant evidence of alteration in the level of the enzyme ribonuclease activity in cancer. Current studies reveal that 80% of all cancer patients have alteration in ribonuclease activity and that individuals known to be at high risk for the development of cancer also demonstrate significant alteration of ribonuclease activity. It is noted that while elevation of serum ribonuclease exists within the cancer state and appears to be independent of clinical status (relapse, remission, or cured), diminished activity is found within the tumor itself. Animal models are reviewed which demonstrate that ribonuclease activity becomes elevated in the murine species subsequent to the transplantation of tumor and following the infection of the host with oncogenic virus. The occurrence of elevated ribonuclease activity in high tumor incidence strain mice long before the development of overt tumor is alos discussed. To date it is not possible to assign a specific function to the changes in the level of ribonuclease in connection with the cancer state. However, evidence indicating that tumor chemotherapy is generally associated with early elevation of ribonuclease activity within the tumor cell suggests that increased ribonuclease activity may play a role in the process by which the host restricts neoplastic transformation. The potential of this enzyme as a biochemical marker in cancer is discussed.