Cathepsin B is a lysosomal cysteine protease whose activity has been
implicated in a variety of physiological and pathological states including the
development of lung disease and the progression of cancers.
Cathepsin B has been implicated in the pathogenesis such lung diseases as
emphysema and chronic bronchitis. Although no direct associations between
cathepsin B and cystic fibrosis are evident, cathepsin B may be implicated to the
disease progression through the diseases associated elevation in neutrophil elastase
activity.
The expression, post translational processing and targeting of cathepsin B is
frequently altered in transformed and malignant cancer cells. Associations between
malignancy and cathepsin B have been reported for human colon, breast, prostrate and
bladder tumours (Keppler and Sloane, 1996). Cathepsin B could have a role in the
detachment of cancerous cells from the tumour, and lead hence into metastasis.
MacKenzie (1995) identified a 19 nucleotide insertion within intron 7 of the
human cathepsin B gene. Sequencing of a B allele also revealed a nucleotide
substitution of G to C at position 319 in intron 7. This study reports that this
substitution occurs in all B allele homozygotes tested and that polymorphic linkage is
present between the absence of the 19 nucleotide insertion and the nucleotide
substitution within the B allele.
This study also reports the screening of 19 normal DNA samples, 30 DNA
samples from cystic fibrosis patients, and 22 colon carcinoma tissue DNA samples (all
samples unrelated). A allele frequencies were determined to be 0.62, 0.65, & 0.64
respectively. Chi-square analysis revealed no significant (p=0.99) difference between
normal, cystic fibrosis and colon cancer sample populations. The two alleles have
been shown to conform to Hardy-Weinberg population distribution within each
sample population so are thought to be stably inherited according to Mendalian
segregation. Studies have indicated that cathepsin B has multiple forms generated by
different cell processing of RNA and glycosylation of the precursor protein. These
polymorphisms have been shown to introduce a potential alternative splicing site
within intron 7 which, if functional would produce larger sized mRNA. These
polymorphisms also have the potential to interfere with the existing intron 7/exon 8
splicing site. This study reports the development of a RNA extraction technique from
human blood, and the design and partial optimisation of reverse transcriptase-PCR
CRT-PCR). These techniques will be used in the future to study mRNA derived from
homozygote individuals blood, and observe any differences in the length or amount
of mRNA between the 2 alleles.[Show full abstract]
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