Upregulation of Leucine Zipper Protein mRNA in Hepatocellular Carcinoma Associated With Poor Prognosis

BACKGROUND

Leucine zipper protein (LUZP) plays key roles in development. Overexpression of LUZP was documented in several types of solid tumors. In this study, expression of LUZP messenger RNA (LUZP mRNA) in human hepatocellular carcinoma (HCC) was examined, and the correlations of LUZP mRNA level with patients' characteristics and prognosis were also investigated.

METHODS

Total RNA was extracted from HCC and paired noncancerous liver tissues of 77 patients. Expression of LUZP mRNA in the tissues was determined by real-time quantitative reverse transcriptase polymerase chain reaction. Using average LUZP mRNA level in noncancerous liver tissues as the cutoff, patients with HCC were categorized into high-expression group and low-expression group. Correlations of LUZP mRNA with clinical parameters were analyzed. Overall survival of the patients in the 2 groups was analyzed by Kaplan-Meier method.

RESULTS

The LUZP mRNA level was significantly higher in HCC samples than in the noncancerous liver tissues (1.87 ± 0.11 vs 0.58 ± 0.05, P < .01). Significant differences were found between the 2 groups in terms of portal vein invasion, Tumor Lymph Node Metastasis (TNM) stage, and recurrence of HCC. The current study failed to find significant differences between the 2 groups in clinical characteristics such as age, gender, lymph node metastasis, hepatitis B virus infection, family HCC history, and alcohol intake. Overall survival in high-expression group was 12 months while that in the low-expression group was 34 months (P = .03).

CONCLUSION

The LUZP mRNA is a prognostic indicator in HCC, and overexpression is associated with poor prognosis in patients with HCC.

The cytoplasmic Purkinje onconeural antigen cdr2 down-regulates c-Myc function: implications for neuronal and tumor cell survival

Paraneoplastic cerebellar degeneration (PCD) is a disorder in which breast or ovarian tumors express an onconeural antigen termed cdr2, which normally is expressed in cerebellar Purkinje neurons. This leads to an immune response to cdr2 that is associated with tumor immunity and autoimmune cerebellar degeneration. We have found that cdr2, a cytoplasmic protein harboring a helix-leucine zipper (HLZ) motif, interacts specifically with the HLZ motif of c-Myc. Both proteins colocalize in the cytoplasm of adult cerebellar Purkinje neurons, and coimmunoprecipitate from tumor cell lines and cerebellar extracts. cdr2 down-regulates c-Myc-dependent transcription in cotransfection assays, and redistributes Myc protein in the cytoplasm. Disease antisera from six of six PCD patients specifically blocked the interaction between cdr2 and c-Myc in vitro. These data indicate that cdr2 normally sequesters c-Myc in the neuronal cytoplasm, thereby down-regulating c-Myc activity, and suggest a mechanism whereby inhibition of cdr2 function by autoantibodies in PCD may contribute to Purkinje neuronal death.

A post-transcriptional regulatory mechanism restricts expression of the paraneoplastic cerebellar degeneration antigen cdr2 to immune privileged tissues

Paraneoplastic cerebellar degeneration (PCD) is believed to be an autoimmune disorder initiated by the ectopic expression of a neuron-specific protein in breast and ovarian tumors. PCD antisera was used previously to identify several cerebellar degeneration-related (cdr) genes encoding putative PCD antigens. We have found that the cdr2 gene, which encodes a cytoplasmic leucine zipper protein of unknown function, is expressed in PCD-associated tumors, whereas other cdr genes are not; thus, cdr2 encodes the PCD tumor antigen. To determine whether the expression pattern of cdr2 is consistent with its proposed role in PCD, we have isolated the mouse homolog and examined both the mRNA and protein distribution in adult tissues. We have found that cdr2 mRNA is expressed in almost all tissues, whereas the protein is expressed only in the brain and testis. Within the brain, both the cdr2 mRNA and immunoreactivity are confined primarily to neurons in the cerebellum and brainstem, the regions most affected in PCD. These results suggest first that the tissue-specific expression of cdr2 is regulated at a post-transcriptional level. Moreover, because the brain and testis are considered to be immune-privileged sites, the expression pattern of cdr2 is compatible with the autoimmune model of PCD pathogenesis.