Organization and Significance of LINE-1-derived Sequences in the 5’ Flanking Region of the Factor IX Gene

Limitation in use of heterologous reporter genes for gene promoter analysis. Silencer activity associated with the cloramphenicol acetyltransferase reporter gene

Various heterologous reporter genes have been widely used for the functional characterization of gene promoters. Many such studies often found weak to very strong silencer activities to be associated with specific parts of the basal promoter or further upstream regions. In this study, we carried out a systematic study on human blood coagulation factor IX (hFIX) and anti-coagulant protein C (hPC) genes, previously shown to have silencer activities associated with their 5'-flanking regions containing promoter sequences. With newly constructed chloramphenicol acetyltransferase (CAT) reporter vectors carrying hFIX or hPC gene promoter sequences, we confirmed the strong silencer activities associated with the regions nt -1895 through nt -416 of the hFIX gene or with the region nt -802 through nt -82 of the hPC gene. However, no such silencer activities associated with the specific regions were found when autologous hFIX cDNA, hFIX minigenes, or hPC minigenes were used as reporters in the expression vector system. Relative levels of CAT, hFIX, and hPC proteins produced in the transient assays correlated well with their mRNA levels. Human FIX minigene constructs containing a simian virus 40 (SV40) 3'-untranslated region (UTR) taken from the CAT reporter gene showed no silencer activity, indicating that SV40 3'-UTR sequence of the CAT reporter gene does not contribute to the silencer activity. Expression vectors constructed with the beta-galactosidase gene under the control of hFIX gene promoter sequences also showed no silencer activity associated with the region nt -1895 through nt -416. These findings indicate that silencer activities associated with specific regions of promoter sequences as analyzed with CAT reporter genes may represent artifacts specific to the CAT reporter genes. Our findings strongly suggest a need for re-examination of promoter characterizations of many eukaryotic genes, which have been studied to date with CAT reporter genes.

Genetic mechanisms of age regulation of protein C and blood coagulation

Blood coagulation activity in humans increases with age. We previously identified two genetic elements, age-related stability element (ASE; GAGGAAG) and age-related increase element (AIE; unique stretch of dinucleotide repeats), which were responsible for age-related stable and increasing expression patterns, respectively, and together recapitulated normal age regulation of the human factor IX (hFIX) gene. Here we report the age-regulatory mechanisms of human anticoagulant protein C (hPC), which shows an age-stable pattern of circulatory levels. The murine protein C gene showed an age-related stable expression pattern in general agreement with that of the hPC. Through longitudinal analyses of transgenic mice carrying hPC minigenes, the hPC gene was found to have a functional age-related stability element (hPC ASE; CAGGAAG) in the 5'-upstream proximal region but was found to lack any age-related increase element. Three other ASE-like sequences present in the hPC gene, GAGGAAA and (G/C)AGGATG, also bound nuclear proteins but were not active in the age regulation of the hPC gene. Functional hPC ASE and hFIX ASE were apparently generated through convergent evolution, and hFIX ASE can fully substitute for the hPC ASE in conferring age-related stable expression pattern of the hPC gene. In the presence of the hPC ASE, hFIX AIE can convert the age-stable expression pattern of the hPC gene to a hFIX-like age-related increase pattern. These results support the universality of ASE and AIE functions across different genes. Clearance of hPC protein from the circulation was not significantly affected by age. We now have established the basic mechanisms responsible for the age-related increase of blood coagulation activity.

Genetic mechanisms of age regulation of blood coagulation: factor IX model

Blood coagulation capacity increases with age in healthy individuals, apparently because of increases in the plasma concentration of most procoagulant factors. This phenomenon may play an important role in the advancing age-associated increase of cardiovascular diseases and thrombosis. Through longitudinal analyses of transgenic mice, we recently identified 2 critical age-regulatory elements, AE5' and AE3', which are together essential for age regulation of the normal human factor IX (hFIX) gene. AE5', present in the long interspersed repetitive element-derived sequence of the 5' upstream region, containing polyomavirus enhancer activator-3 or a closely related element, is responsible for age-stable expression of the gene and functions in a position-independent manner. AE3', present in the middle of the 3' untranslated region, is responsible for age-associated elevation of hFIX mRNA levels in the liver. Presence of both AE5' and AE3' is needed to recapitulate normal age regulation of the hFIX gene. Because factor IX clearance from the circulation is not significantly affected by age, age regulation of hFIX levels is achieved primarily by a combination of stabilization of gene transcription and age-dependent increases in the mRNA levels, which are presumably due to increasing mRNA stabilization. The stage is now set for further systematic studies of the genetic and molecular mechanisms of age regulation of other key coagulation and anticoagulation factors in hopes of understanding the overall age regulation of blood coagulation.