  [Abridged] We present the analysis of ISOCAM-CVF and NIR photometry data of
the HII region complex N4 in LMC. The aim is twofold: 1) to study the
connection between the ISM and the star content of this region; 2)to
investigate the effects of the lower than galactic metallicity on dust
properties. A dust features -- gas lines -- continuum fitting technique on the
data, allows the production of images in each single emission and the detailed
analysis of dust, and ionized gas. The NIR photometry provides, for the first
time, information on the stellar content of N4. The images in single dust
feature bands and gas lines clearly show that the HII region core is completely
devoid of the carriers responsible for the Aromatic Features (AFs). On the
other hand, the ionized gas arises almost completely in this dust cavity, where
also the two main exciting stars of N4 are located. We find evidences that the
effect of lower than Galactic metallicity on the carriers responsible for the
AFs, is not to prevent their formation or to modify their chemical properties,
but to enhance their destruction by the high and hard ISRF. We show that this
mechanism is more efficient on smaller dust particles/molecules thus affecting
the dust-size distribution. We argue that effects on dust--size distribution,
rather than thedifferent dust properties due to a lower metallicity, should be
taken into account when analyzing more distant relatively low metallicity
galaxies. Finally, the analysis of the stellar content of N4 reveals 7 stars: 4
reddened O MS stars and 3 stars with envelopes. In particular, one of these,
seems to be an Ultra Compact HII region containing an embedded YSO.
