MicroRNAs for Enhancement of CHO Cell Proliferation and Stability: Insights from Neuroblastoma Studies - MicroRNAs as Tools in Biopharmaceutical Production - page 88

6.1 Introduction

The Chinese hamster ovary cell line (CHO), derived by Puck et al. in ( 1958 ) has
been widely used in the field of somatic cell genetics to identify novel genes through
mutation analysis. A plethora of drug resistant and auxotrophic recessive genetic
variants could be isolated at high frequency from this cell line (Siciliano et al. 1978 ;
Siminovitch 1976 ). CHO cells have a very rapid rate of proliferation and possess a
karyotype where one haploid set of homologues have normal banding patterns and
a second set that have undergone considerable rearrangements to form stable and
well defined marker chromosomes. The chromosome rearrangements have led to
hemizygosity for some genomic regions that has contributed to the ease at which
some recessive mutations can be isolated (Deaven and Petersen 1973 ). Numerous
studies were undertaken to map genes to the rearranged chromosomes of CHO cells
to further investigate the molecular mechanisms yielding the high frequency of CHO
genetic variants, and to identify regions of synteny with the human genome (Adair
et al. 1983 ; Adair et al. 1984 ; Stallings et al. 1984a ; Stallings et al. 1983 ; Stallings
et al. 1982 ; Crawford et al. 1985 ; Stallings et al. 1984b ).
CHO cells have become the cell line of choice for the biomanufacturing of pro-
teins because of the ease at which they can be genetically manipulated and because
of their outstanding growth characteristics. It is therefore not surprising that consid-
erable research has been undertaken to further enhance the growth characteristics of
CHO cells for biotechnology purposes (Clarke et al. 2011a ; Clarke et al. 2011b ),
including the use of microRNAs (miRNA) to further manipulate the phenotypic
features of CHO cells (Barron et al. 2011 ). MiRNAs are tiny 20-22 nt sequences
processed from much larger sequences that negatively regulate gene expression post-
transcriptionally (He and Hannon 2004 ). These miRNAs act by binding to regions of
homology on the 3 UTRs of specific mRNA sequences, causing either the degrada-
tion or translational inhibition of the mRNA sequences on the RNA induced silencing
complex (RISC). MiRNAs play major roles in normal physiological processes, and
their dysregulation is intimately associated with the development and progression
of many forms of cancer (He et al. 2007b ). This is particularly true of the pediatric
cancer neuroblastoma (Stallings 2009 ; Stallings et al. 2011 ; Stallings et al. 2010 ),
which has been the subject of research in my laboratory. MiRNAs can act in a posi-
tive oncogenic manner, promoting cell division by targeting tumor suppressor genes,
or as tumor suppressors by promoting apoptosis, cell differentiation or senescence
(summarized in Fig. 6.1 ). Often the phenotypic effects of miRNAs are cancer cell
type dependent, having completely opposite effects in different cancers.
Although the identification of miRNA targets that decrease cancer cell viability
are exactly the opposite traits from genetically engineering CHO cells for increased
proliferation, the same target miRNAs could be of interest for improving pheno-
typic features such as resistance to apoptosis, shorter cell cycle times, etc., for
biotechnology purposes. This chapter is to review some of the lessons learned about
miRNAs in the cancer field, with particular emphasis on the relevance to problems
in biotechnology.